Old-School Class Idea: Fighters=Thieves

Between my in-progress read-through of Holmes Basic (especially this part), my proposed method of separating race and class in LotFP, my re-reading of this post from James Raggi's blog, this Google+ discussion about Thieves in Holmes Basic, this blog post about the supposedly "preternatural" aspect of Thief abilities, and a whole bunch of posts and discussions all over the Internet about whether or not Thieves suck (like this and this and this and this), I've come to a realization:

Mechanically speaking, I don't really like either Fighters or Thieves all that much in most or all of the old-school D&D (and D&D related) games that I'm familiar with, but I think I might like them a whole lot if they were combined into one class.

My proposal is this: Remove the Thief class (or equivalent) Keep the Fighter exactly the same as it is in terms of Fighter class abilities, equipment use, HP, XP, saving throws, etc., except that the Fighter can also use all Thief abilities (or skills or whatever) as if they were a Thief of the same level. In LotFP, they would get skill points like a Specialist. In OD&D + Greyhawk or Holmes Basic or AD&D or whatever, they would use the percentages from the Thief table for picking locks and hiding and stuff, and they would be able to sneak attack/backstab.

Optional caveats: You could make it so that only human Fighters get these Thief abilities, since demihuman Fighters already have other extra abilities in many games. This is similar to what I suggested in that aforementioned post about separating race and class in LotFP. Also, Thieves gain the ability to use magic scrolls or wands in some versions of the game. If the idea of a Fighter being able to do that bothers you, it would be easy to disallow it.

(Please keep in mind that I'm specifically thinking about pre-Wizards of the Coast D&D and OSR games based on old-school D&D. I don't know that I'd want to make this change in D&D 3.5, for example.)

Here are some objections I could see being raised, and my responses.

"Wouldn't this make the Fighter/Thief too powerful compared to the other (core) classes?"
 I could maybe see this being the case in LotFP, since the classes are so hyper-specialized and niche-protected in that ruleset, but even so, the idea of a Fighter who also has a knack for Languages or Bushcraft or Stealth is deeply appealing to me.
Regarding old-school D&D, I often hear complaints that the Cleric is way more powerful than the other classes (or at least the core ones, if you're talking about AD&D or OD&D with all the Supplements and such). I also hear a lot of people say that both the Magic-User and the Cleric have way more potential for growing in power than both the Fighter and the Thief. While initially weak in many ways, even the Magic-User is arguably more powerful overall than other classes. Perhaps by combining the Fighter and Thief, the resulting class would actually catch up to the Cleric and Magic-User in terms of individual utility. If you allow Paladins and Rangers, this house rule might also help the Fighter differentiate itself from those classes a bit more.
Also, both Fighters and Thieves are already able to use magic swords and other magic weapons in many versions of the game, and the guy clanking around in full plate is probably not going to be that sneaky regardless of Thief abilities unless they strip down, so I don't think this house rule would throw things off too much in that regard.

"Wouldn't a Fighter be too busy focusing on fighting during their formative training to also pick up Thief training, or vice versa?"
In real life, soldiers train not only in fighting, but in wilderness survival (bushcraft), stealth (and attacking from stealth while targeting vital organs), climbing, searching for and disarming or avoiding traps, and numerous other skills that would fall under the mantle of the Thief in D&D (and the Ranger, for that matter). One can be good at fighting without devoting every single minute of one's life to that pursuit alone. It seems weird to me that the Fighter is often portrayed as being good at nothing but fighting, aside from the basic things that any adventurer of any class should be able to do. It seems logical to me for someone who intends to go dungeon delving to try and pick up Thief skills, since they could be crucial for success.

"Aren't Thief skills supernatural or almost-supernatural abilities that deserve a class of their own, or that would be too hard for someone to pick up without sole dedication to those skills?"
This is a perfectly valid and very cool way to imagine Thief skills, but it is not the only way. One could be much better at certain (usually non-combat) physical activities than most people while still only acting within the realm of non-magical capabilities - in real life, we call these people athletes, experts, and prodigies. I don't see why dexterity in combat couldn't also translate to dexterity in picking locks, or why the upper body strength, bodily coordination, and expert balance of a sword-fighter couldn't be transferable to climbing, given practice. Fighting skills can be transferable to other activities, and vice versa.
Besides, in my mind, Fighters are often the action heroes of D&D, the Schwarzeneggers and Van Dammes of the dungeon. Those characters aren't just good at fighting, but also at feats of agility that one might consider to be in the Thief's wheelhouse - they tend to do a lot of climbing and sneaking and running from explosions. And the Thief, on the other hand, is often thought of as an Indiana Jones type of character, and Dr. Jones sure knew how to handle himself in a fight, to the point that I tend to think of his movies as action films, among other things. And don't forget the pop-culture ninja, who is an unparalleled warrior in straight-up combat and a master of stealth, sneak attacks, climbing, disguise, using and avoiding traps, finding hidden things, and spying.

"Wouldn't this be against the genre conventions of the fiction that inspired D&D (or fantasy fiction in general)?"
Maybe, but I'm not so sure about that. According to the Giants in the Earth series in Dragon magazine, Gary Gygax's Conan write-up in Dragon #36, and the stats in Gods, Demigods & Heroes (and supposedly Deities & Demigods, although I don't have that right now), many classic Sword & Sorcery heroes are both Fighters and Thieves: Conan, Moonglum, Fafhrd, the Gray Mouser, Kane, Shadowjack, Muirtagh, Captain Blood, and Dark Agnes. To my great shame, I don't even know who about half of those people are, but they're apparently from the kinds of stories that directly inspired D&D.
Besides, in the classic kind of "kill things and take their stuff" campaign, isn't everyone really a Thief at heart?

"Wouldn't this make AD&D style multiclassing and dualclassing obsolete as far as a Fighter/Thief combo is concerned?"
 Yep. I don't really care

"Shouldn't you come up with a new name for this combined class?"
 Yeah. I'd love to hear some suggestions.

"Do you think you're the first person to think of this?"
Not at all. I know someone by the name of Lorgalis came up with the idea before I did in a really cool post in a cool thread, for example. To be fair, I think I did come up with this independently before seeing that someone else had already suggested it, but it's such a simple idea that I didn't expect to be a very original thinker here.

"I just don't like this idea for reasons of flavor or aesthetics."
That's fine. It personally doesn't bother me (quite the opposite), but I know this idea just won't be fun or appealing for everybody. I think it would put an interesting spin on the rules without compromising too much in terms of flavor, but it's obviously fine to disagree with me. Really, I'm just addressing some pet peeves of mine in terms of both game balance and flavor, and my pet peeves might be beloved aspects of the game to others.

Besides you could play a Fighter/Thief in so many different ways. You could be a typical platemail-clad walking tank who also happens to be particularly attentive when searching the environment. You could be a member of the Thieves' Guild who happens to also be handy with a blade. You could be a ninja, always looking to gain the element of surprise. You can be a scout, a swashbuckler, a bandit, a mercenary, or a particularly clever knight. You can lean more toward the Fighter end of the spectrum or the Thief end, based on your equipment and preferred tactics. I don't think extra HP and a to-hit bonus ruins the flavor of the Thief, and I don't think being able to climb and sneak and listen through doors and look for traps would ruin the Fighter. Even picking locks are disarming traps don't seem to me like things that are necessarily foreign to a tough, smart, well-rounded warrior. Or even a stupid warrior who managed to pick up some tricks on the mean streets of Phlan - they managed to pick up fighting, after all.

I'd love to hear opinions and suggestions if anyone is interested.

EDIT: If you want to nix the Thief but don't like my way of doing it, HERE is another suggestion that I like from Vaults of Nagoh. Also, I want to note that I don't hate the Thief; I just don't usually care for the specific mechanics of the class. Likewise, I don't hate the Fighter, but I feel like the Fighter is often pretty boring or limited in terms of abilities in comparison to the other classes. This is just a possible way of addressing that, along with my belief that it would make sense for Fighters to have some of the skills that are traditionally in the domain of the Thief (as well as some other skills). Finally, I should note that the main games I had in mind for this suggestion were OD&D, Holmes Basic, and Lamentations of the Flame Princess, but it could probably apply to many others, too.