Well, the concept of a ban list seems ripe for abuse. We have to trust someone to tell us canonically who the bad nodes are, people can slap a fed honeypot node label on you for not going along with something.

What we need to do is design the system such that a bad node can do nothing but participate in the network. Just like the mining incentive structure with nakamoto consensus. Dandelion++ is supposed to do that, at least for everyone broadcasting their transactions only to initial nodes they know and trust. I don’t know how to do that, but a blacklist is a dangerous stopgap.