1: It’s extremely common for people to be biased in favour of a group they’re part of, since they benefit from that support.

2: It’s also extremely common for group members to pretend to be outsiders when supporting their group, precisely because of (1). “Oh well, if this person is supporting the group despite being an outsider, they must be super-altruistic, and therefore their cause must be super-righteous.”

3: If a group meets with widespread disapproval, then one way to silence external support for it is accusing the supporter of (2) - suggesting that not only are they one of the hated group, and also showing how dishonest the group members truly are.

4: Dunking on out-group members - especially via (3) - strengthens the bond of the in-group.