How about a concerted effort to figure out the crossover of membership of police/military/ice etc… and these facebook groups, and then dishonorably discharging/firing with prejudice all these a-holes?
Then set up a bunch of decoy groups to attract the same. Make it so racist a-holes never know if the group they’re joining is quite possibly a fake designed to lure them out.
If you’re not going to ban this sort of crap wholesale, then at least use it to root out the rot within.