Banning someone from an event should be a final resort, used only after every other option has been exhausted.
If someone has been warned and still causes trouble then a ban might be an option. But if said person has been banned just because they're not friends with the TO then that is out of order. If you just want to play your friend set up a closed casual play day not a tournament.
People are always going to clash but the point of being a grown adult is to understand how to react like an adult in these situations.
I'm sure there are plenty of other factors to this that I don't know but on the surface banning someone who has done nothing wrong because you don't like who they are is only a short step away from banning someone because you don't like what they are.
(not 100% any of that is actually English or makes complete sense but its been a long day)