If someone's a bystander...

If the person is actively supporting the bully, then that person is also a bully, not just a bystander. He/she forfeits any right to consideration and courtesy at that point. Bullies are loathsome even if they're just secondary bullies going along with the big bully.

As for helping a genuine passive bystander who later becomes the target of a bully, I'd like to think I'd stand up for the person. A lot of people watch a bully do their shit because they worry that if they speak up, they become targets too. What they don't realize is that if everyone who thinks it's shit speaks up, the bully can't go after six or twelve or twenty targets. The balance shifts; the bully becomes the weakling who can't take action any more.

I just swing away.

Why would I help bully someone? Well unless of course they are being an annoying cunt to everyone. In which case I would probobly find them irritating and ignore anything bad happening. If it was an innocent person I would probobly not join in.

What goes around comes around.

The satanist would bully them both and smile with joy for he has achieved his revenge.

yes, i treat people the same way as they treat me.

If the guy helps the bully, next time I'll beat up his bully, so I can bully him!
Eye for an eye... (In my case it's an eye for two!)