Well, it's not like they are fighting the normal criminals. These are people with powers who were using their abilities to hurt other people. Pretty much any of the villains they killed were trying to hurt either the Senshi or innocent civilians.

But what of those who had been corrupted on the basis of their past lives (Beryl) or those who were but innocent bystanders (Kaolinite)?

Mind you, this can be engaged between different adaptations, but I'm not so sure how I feel about the senshi basically taking the law into their own hands and there being no repercussions for it.

I understand the threat, but you'd think that there would be more of a mundane reveal of the dangers these enemies pose as opposed to it being a secret mission of sorts. Perhaps what we don't see are those very effects on the day to day lives of common people.

They confronted Kaolinite and she turned into a Daimon and attacked them. It's not like they knew her backstory. And for all they knew, when she turned into a Daimon, that was all that was left of her (manga and in extension, Crystal, is a little more cynical than 90s anime in regard to death or redemption).

I can't really speak for Beryl since the idea of past lives influencing present is shaky grounds for me. But for her death in the manga, it's simple. She was killing Sailor Moon with her hair. Sailor Venus tried to free her, but cutting the hair didn't help so she did what she had to in order to save her princess.

And as to taking law into their hands, again supernatural beings threatening the world kinda falls out of the usual jurisdiction.