And that won't change anything. Do some god damn basic math and use your noggin:

User A used their stake for no benefit other than to be a jerk.

Why would A give a fuck at all if anyone downvoted the spam he made ONLY to jump through a hoop so that they can freely be a jerk?

You're literally saying that making serial downvoters spam will make them reconsider being a serial downvoter, but you avoid the glaringly obvious, or that they don't give a fuck about someone downvoting them. Heck I can see them even embracing being downvoted simply because it might tickle them to see people"retaliate", aka Waste Their Fucking Voting Power.

It's like I'm the only one who can see this glaringly obvious conclusion and no matter how I explain it all you're fixated on is the idiotic thought that you can stop Downvoting by making them post so they MIGHT be downvoted, and o yeah, because downvoting will surely stop Downvoting.