If it disturbs you to see people speak ill of the dead, it might be time to examine the apparent compulsion to speak well of them. There will always be those who mean so much to us that we have to eulogize them. Of course. Observances of death are for the living, including the mourners.
After that, well, we always have the option to say nothing. We take it too rarely. Even more rarely do we think about how our words may prompt responses, how our statements invite argument.
You don’t owe it to the dead to speak well of them. They can’t be helped or harmed by it. They’re dead. Your words, if any, are for the living. That includes the people injured by the dead. If you don’t want them to speak of those injuries, consider simply not speaking praise that erases them. It’s easier than you might think.