A number of years ago I saw an article on Revach.net regarding cremation that addressed this issue. I cannot locate it.
If one’s relative lived his/her whole life totally unobservant of mitzvos and wishes to be cremated, is there a reason to discourage it
You should do everything in your power to discourage him from being cremated. The way he lived his life is irrelevant to the way he is buried.
Gesher Hachaim 2 Chap 13