As far as we know today, sex for pleasure's sake is one of the unique characteristics of hominid species. For bonobos specifically, it's a means of social cohesion.
Don't you mean the other way? I'm pretty sure all animals have sex because they enjoy it, not because they want to procreate - since they most certainly don't even know what procreation is. So sex for procreation is something that only humans are able to do.
I don't know why you're sure of that opinion: it is well beyond current scientific evidentiary support. And sex in some species (e.g. ducks) appears deeply unpleasurable for at least one of the participants.
But homosexual behavior is widespread across animal species, which does undermine the parent's case.
So somewhere there's a gay duck having a bad night.
Some studies suggest that Dolphins have sex for pleasure too
Some graduate student stories I've heard suggest that some Dolphins may (like Ariel?) be "skinnies".
You’ll have to explain your post a little more. I’m afraid I don’t get the “skinnies” reference
If furries like creatures with fur, skinnies would like creatures with skin.
(this was not a Starship Troopers [book] reference)