... I could make a completely Pacifistic character-diplomat, without any killing on my hands(physically, or by some other means like frenzying someone).

Fallout and Fallout 2.

Played them.)
I don't remember it well, but could you do it in Arcanum?

Can't remember that about Arcanum, but I suspect that if you did the right decisions and were ingenious enough, you probably could. Or not, I never tried pacifist in that game.

I think there was a way to do it in Deus Ex, though (if my memory doesn't completely fail me).

I will check Arcanum, then, maybe you could combine diplomacy and stealth, using the latter where the former is impossible.
Yeah, i seem to remember that about the first Deus Ex, and I've never played it. Maybe it's time.

Yep, using a mix of stealth, non-lethal weapons, and glitches.

Don't remember those glitches.