The thing about TKing is, that it is actually quite hard to votepoll such behavior, as, face it, would you click 1 or 2 if opponent team (enemy) had a guy that is killing them (your enemies)?
About accidental TKs, the situation i see most often are frag hungry people, when i dehorse a guy, i do not even bother going after him as i get usually to half HP by my teammembers if i try to...Also, hitting a dead guy makes your blade or whatever go through, so if you see dead body falling to the ground, try to sneak in the block to stop your swing and not kill your friend in sword.
Accidental TKing happens quite a lot, as new players are joining the game (i presume, as when i was beginning, i had loads of difficulties hitting the correct guy
), but with time they will get better.
Some sort of penalty would be most welcomed, as now usually when i land a TK i apologize (sometimes get killed in the process) and i am pissed that i noobed out, i believe most of players do the same, but still, once you make mistake, nothing wrong to pay for it
(i have seen a guy deliberately TK and return TA all the time, luckily he got banned
)