[Warrior of the Light]

There will always be trolls. Like everywhere else on the internet, don't feed them.

Stay away from pointless discussions or let him make a fool of himself towards the other participants. You don't have to 'beat' anyone; the internet is not a game that can be won.
If you like the other people there, talk with them and don't let Frank tell others what to think of someone else. Everyone's free to make up his own mind. Make sure everybody knows this.

If his power over the others is too big, then yes, find/form a new group. There are billions of people on this planet. Don't let a few people who you've never even met screw up your day.