People now think about people that have sex with dead bodies similarly to the way people used to feel about gays. We haven't become a nation of tolerance, we've just moved the goal posts and declared victory.
Changing the public perception of necrophilia will require more drastic change than the acceptance of gays, or even furries. You'd need to get everyone to see a corpse as an object rather than their dear Aunt Sally. You'd be going against not just centuries, but
all of human history. We've been burying the dead to keep just this sort of thing from happening - desecration of the corpse - since we've been "us."