Most of the time, the critics are missing Fortgang’s point. He didn’t express resentment at having to consider the perspectives of women and minorities; he didn’t claim to be vicariously oppressed because of the travails of his grandparents; he didn’t deny the existence of racism or sexism or similar evils. And he didn’t deny that he’s privileged.
What he actually said isn’t that hard to fathom, because he announced his target in his very first sentence: the use of the phrase “check your privilege” to “strike down opinions without regard for their merits, but rather solely on the basis of the person that voiced them.”
It’s perfectly reasonable to ask someone to consider whether their arguments or observations reflect the biases of privilege. Perhaps an upper-middle-class white man’s claim about the hardships of poverty or the prevalence of racial discrimination reflects a lack of experience of those things, for example. But all of us need to ask ourselves whether our views are skewed, regardless of how privileged we are, because there are many possible sources of bias. Fortgang is quite right to complain that being obsessively on the lookout for white male heterosexual bias can obscure more than it reveals, in part by ignoring how much heterosexual white men can differ.