You forget that these people find the very existence of brown and black people exhausting. As a result, their stupid little safe space being full of political nonsense is still less stressful to them than the real world.
A quality shitpost is supposed to be offensive without punching down. It obviously achieves the first criterion for you. I would argue that the second criterion is also met because the offensive statement is immediately followed by self deprecation.
Is that desirable in a dessert?