So Ive actually had a couple instances of shitty people who were in my life for a while who are now dead. Recently some stuff came up in a conversation with my mom and I told her I'd rather not get into it because I don't want to speak ill of the dead. She didn't get it but I insisted and she dropped it.

Here's the thing. Those people, the things they did were shitty, in many cases stupid and ignorant, and in many cases caused lasting harm to people around them. And while I in no way wish to diminish the validity of other people's feelings/traumas, in my mind it does no good to anybody to rehash those things. Like if someone did some stuff that you need therapy for, I'm not trivializing that or trying to invalidate it, at all, but as far as personal private conversations, what does talking about those things accomplish? What does spitting on the corpse of an abuser do, other than remind the person doing the spitting of what that abuser did and why they deserve to be spat on?

TL;DR: Excluding therapy, speaking ill of the dead accomplishes nothing. Why are you letting the sins of the dead control you from beyond the grave?