We do not need our bodies once we leave this world regardless of what you think happens after we die. We should be focused on curing diseases and extending the life of living humans. Science would go so far if we used human bodies after death instead of requiring people to give consent to something they don’t need.
i’m sure there’s far more to this but here’s one interesting article on the subject
A body donated to science - but used to test bombs: https://www.bbc.co.uk/news/world-us-canada-49198405
of course this is less of a worry in countries other than the US. But tbh if i lived there i’d still give the ok as there’s still a chance of my corpse being put to some better use than ash or worm food