People who follow individualism, from what I've seen and experienced, are simply the ones who are not joining the tribe that has managed to get them hating the other tribes the most. They actually have at least one belief they could agree on with each tribe, but also have one or more beliefs that would get them attacked or banished by each tribe. The latter always wins, so all tribes hate the individualist for not hating the other tribes enough.

Tribes that talk about individualism as being a great strength and then punishing you for not conforming are not really that individualistic, in my opinion.

It's not the individualists who are the problem. They are the ones getting ostracized by all for daring to have a set of beliefs that don't conform precisely with any of the tribes warring with each other. They would prefer that the tribes disbanded and everyone was free to believe what they wanted without fear of pissing off people they have never met. Most people, as far as I've seen, just want to live their lives believing what they like without getting attacked out of the blue one day. I remember when you didn't know what others believed and could spend a lot of time with your favorite drink in hand finding out, arguing, agreeing, and leaving in peace. Well, at least most of the time.