Disregarding the fallacy of #2 (Action Movies =/= Real Life. Not even close); Attracted to Martial Arts and Action Movies does not mean skill in violence, stealth, and/or killing.
Hell, a guy skilled at sneaking up on someone and kicking their ass wouldn't necessarily make a good assassin, as there is a difference between beating someone into a coma, and actually knowing 100% beyond a doubt that you just killed the person.
Geeks are also attracted to strong moral systems. See: Star Trek, Star Wars, and so on. A lot of sci-fi is written from the viewpoint of attempting to bridge gaps of understanding with alien species who simply do things different ways. Sure, there's also stuff written about blasting them into oblivion, but even then it's not done to the full extent that it should be done (That is, if you're at war with an alien race, you know where their homeworld is, and you've got access to faster than light engines... strap those to an asteroid, fire it at their planet, problem solved. Screw dogfighting with one-man fighters.) with the assumption being that in the future, there will be peace between the Humans and the Klgha-dla'dar of Ortega Alpha 9B or whatever.
Just because I understand angles and know exactly where I need to bank the ball to hit the other balls and make them go into the holes doesn't make me good at pool. I know what I need to make the cue ball do.. I just don't know how. Same thing with knowing the physics of a shootout.. doesn't matter if you can't aim.
So.. no, I'd think that a geek wouldn't make a better assassin than a baker or a postman. A sociopath, however...