It's like how women who deviate from the feminist line are somehow oppressing other women.  If "the marginalized group is incapable of oppressing the oppressors"--e.g., "blacks can't be racist"--and "people of size" are an oppressed group, it means that, as a member of the oppressed People Of Size group, Trump is incapable of fat-shaming.    Tumblr's ideology only works when you suppress every logical urge that bubbles up from your brain.