how much roadkill is really accidental?

You’re not kidding. We’re so over run with them here in PA that Allegheny county is organizing deer culls. (A lot of animal lovers are fighting it, but the things are goddamned nuisances. I hate deer)

I’ve accidently run over a cat once - hit the brakes but when I started to lose control thought the cat was a better option than me.

I’ve had a friend that (claimed) to have run over a sheep while on a motorbike (he was speeding something chronic)

Neither were “on purpose”

In NZ it is rather common to deliberately run over possums and rabbits deliberately at night night.
Possums will often “freeze” making them a relatively easy target - while a rabbit running away from you down a country road can be aimed for.

Both are pests.

Southern California; Inland Empire. It’s a desert area and I see a lot of jackrabbits but I’ve never seen a deer. I imagine there’s more in NorCal.

Deer are shy of carnivores. If you stare at them and think carnivorous thoughts, they will usually go away, at least while you are there. I tell them, “I want to eat you” when they collect in my backyard and that always disperses them.

It’s a way to get free venison. Up in Maine, for example, if the authorities can’t prove the deer was deliberately hit, first dibs goes to the driver who hit it. Otherwise, some needy family gets it.