A few rules:
1) It should take less time to ban someone than it takes the offender to commit the offence. If you’re spending time engaging in counter-arguments and engaging in lengthy debates, you’re losing the battle. If you’re going to ban someone, don’t get sucked into a lengthy debate about it.
2) You can ban anyone who does more harm than good to the community. There is no law that prevents you from removing any member who isn’t a good fit. If you’re hosting a dinner party and someone is clearly causing trouble, you remove them for the benefit of the masses. They don’t need to have broken a specific rule, they simply need to do more harm than good.
3) Your reasons must be consistent. If someone repeats the same offence and isn’t banned – that’s going to lead to problems. Every ban sets a precedent. If you ignore the precedent next time you’re going to rattle a hornet’s nest.
4) The person you ban might will probably first try to seek revenge. First, they will try to rejoin the community. If that fails, they will try to harm you or the community. Try to imagine, if you were them, what would you do to cause the most harm? Don’t be alarmed, just be prepared.
5) Everyone is replaceable. No figure is ‘too big to ban’. People assume available roles within a community. When you remove a top member, you open a slot for another member to take their place. The success of your community never hinges upon one or two people. You might find the very person you thought was too big to ban was actually holding everyone else back.
Good luck.