I'm not really a hardcore necrophile, but I'm interested in the psychological aspect moreso than anything else. There's just something about the taboo of desecrating a fresh corpse, especially doing so in such a lewd and intimate (or rather, invasive) matter. If the person has been long dead, it's only gross and distasteful, but with a fresh corpse, there's an added layer of disrespect. A recently dead person can't consent, nor can they say no, but at the same time, they're not just an "object", especially not if you knew the person personally, which makes things even more interesting.