I think the tribal thing is interesting but a meaningless distinction when it's such an easy choice like this

The tribes are essentially people refusing free vaccines for no reason vs people who are vaccinated to protect themselves/others

This is one of the easiest cut and dry examples I could think of to justify in-group/out-group behaviour, you shouldn't be forced to tolerate or associate with people making deliberately bad decisions

You could extend this argument to drunk drivers and I think it would hold just as little weight