I wouldn't call that "take the fighter on directly", myself. That's dirty fighting, not "honorable combat".
Exactly. But some are taking "I want to be able to take on a paladin or fighter in combat" to be some kind of heresy. As long as he takes out the opposition the way a rogue should, why is the fact that he's as effective in combat such a problem?
I don't know about 4E, but 1E-3E certainly allows you fight dirty and do more than massive damage via knife attack, and you usually don't need special rules to do it* (though you might need some equipment at times, such as blinding powder). It does, however, depend on the DM being open to more than the school of "I swing my sword" combat methodology.
* You can do some of these tricks as follows:
I'd emphasize the second last line here. It does depend on what your DM lets you get away with, or how flexible he is. I would also point out that all of the options you mention are buried deep within the splatbooks.
An effective way to fight dirty should be in the PHB, and be as much part of the thief as disabling traps, evading damage and using scrolls. There should be an underworld section of the PHB for blinding powder, garrotes, saps, acids, sedatives, caltrops, marbles, blowguns, concealed weapons, and improvised weapons. What is more, these weapons should have rules to do what they do in the real world, namely level the playing field between the rogue and the fighter.
Yes, 4e has powers to blind people, cripple people, stun people and even to knock them out. Given that the rogue can do all that in 4e (I call the rogue the "most improved" class), you can see why I don't want to go back to simply being the fighter's backstabbing buddy and the party helper monkey for traps and locks.
I don't think it'd be bad policy, but you do have to be careful on how it is allowed so it doesn't become SOP (Standard Operating Procedure) to handle every enemy.
I don't see why it would be a problem. A fortitude attack means a risk of discovery if you fail, being able to target only one opponent means you can't use it when the target isn't alone. True, its use in combat might be a problem if the thief uses it in lieu of the backstab ability, but with a 1st level sleep spell and other save or suck/die effects that ship has already sailed.