I also try my best to avoid war as a solution, just was sharing some thoughts, including that 'downvote for downvote' feels like war, unproductive.
But based on this protocol, there are really only a few ways to respond to a downvote, which any other member of this community is free to give. You can ignore it, you can reason with them, you can change your behavior, or you can 'go to war'.
In this case it would be an asymetric war, if you decide to fight - have you considered each of the other options?
Look, there is no problem if he stops his crusade and his stupid assumptions,i think, nobody here is interested in his actions or crazy opinions.
He should solve his problems somewhere else.
Best regards.