Oh I don't think that Jack is better but that's how Kate sees him, and still, he hasn't committed murder no matter the intent; he didn't intentionally take a life.

I guess, that the show clearly stated that anybody, even the best ones, may in certain circumstances become killer though (even Jack could have...).

In the flashback verse, Kate and James were the only murderers I think (Sayid was only a torturer), the others may have caused death but they didn't murder (unless Jin did?), but in the island verse (or in the flashforwards) they almost all became killers. Even Locke killed the girl sent by Widmore (don't remember her name). Sun killed the blonde girl on Desmond's boat.

I don't remember Hugo murdering anyone. Do you?