Would we not, if doing so, become more and more like him?
I don't see it that way, mainly because intent is a major factor or difference to me when judging an act. You can kill and be a monster in one instance, and kill and be a hero in another.
The man did this to her for certain reasons, we would do it to him for completely different ones. In other words, even if we assume its actually bad for some reason, we're still not like him, as our motives are completely different.
One more thing is that the punishment in that case would either be carried out by the victim herself, or someone that has nothing personal with the attacker, so in either cases 'we' as a community don't really have much in common with the attacker.
If you're talking about the victim herself, i personally think revenge isn't a good idea, however there is still a world of difference between her and him, even if she did to him exactly what he did to her, as their motives and reasons for doing the same act are completely different like i mentioned.