When you admit that you are acting more or less blindly, the premise that inaction is immoral falls down.
With which I mean that while I agree that inaction does not render you guiltless, and that it's better to, for instance, sacrifice one of two cojoined twins rather than letting both die, in the Hitler example at this point you're pretty much embarking in a "change time" adventure that might or might not make things better or worse, and thus utilitarian mores don't apply either.
Besides, even assuming certainity, people here are trying to make the point that killing Hitler as a kid would be moral because otherwise you are letting millions die. I agree with you in this, but that wouldn't make killing Hitler any less unjust. Hitler's future deeds don't play any role in this hypothetical scenario, as you are arguing it. If you had to kill, say, Groucho Marx instead of Hitler, it'd remain the same.
I want Greece to go down because every Greek I've met on the internet (all 3 of them) has been an insufferable prick who couldn't stop talking about Alexander the Great and the inevitable reconquest of Constantinople. Plus, not letting FYROM call itself just Macedonia is a dick move.
Greek ultranationalists go into epileptic fits when you remind them that he wasn't Greek, but a Macedonian barbarian. Try it, it's fun.