I mean, this question is not just about normal criminals.
Think like very bad crimes. Like serial killers, rapists, child rapists, terrorists, corrupt officials, terrible leaders, cruel dictators, generals that ignore laws of war, or like people has bad as Hitler. Which of these people do you think deserve a respectful burial, if any.
Is there a level of evilness that you think should not be allowed to have a proper buriel or have their corpses mutilated. Or should everyone deserve a respectful burial regardless of crimes.
I personally don’t even know how to answer this question myself. Like the funeral isn’t even for the dead. Its for the living. So to me, the question seems like, should the relatives of a bad person be allowed to see the corpse treated respectfully. I personally don’t have an answer to this question.
No. Those relatives that have not enabled or supported a monsters actions are of course completely innocent.
And if they want, they can of course mourn the loss of the ability to ever have a nice conversation with that person again.
But a burial is not like mourning in your bed, crying yourself to sleep. There you can accept that you are sad about the loss, even tough the world is a better place without that person.
A bureal however is a public performance that, as you say, is for the living. Not for the dead. It is not useful for mourning, but a ritual to pay the last respects to the deceased person. Not only for their good side, but also for their evil side. And the bigger the burial, the greater the (implied) respect. This holds true in any western/materialistic society, and was practiced in ancient times, where pyramids were built to honor kings, and a bigger pyramid implied a better king.
Therefore holding a large burial for a horrific person signals to the living that you not only miss that person as a friend, but also support their actions and choices in life.