About Vampiric Regeneration on weapons.

[Cabarcos]

I always had doubts about the weapons with vampiric regeneration. It's considered evil to use them or you need to be evil to be able to (or to have UMD).
I've found one sword of this kind with my rogue. He is going to be a ranger in the near future, so he we'll be able to use Blade Thirst on his swords.
What's the difference, if any?
Only an evil Ranger will use the spell?

Thinking about that, I always come to the same conclusion: if someone is stabing you with a sword to kill you, is he/she more evil for recovering some health while doing it? A sword its made to kill, so...