Sullivan is a racist who used his perch at @NYMag to push the idea that Black people are genetically less inteligent, that white supremacist Charles Murray has "legitimate conservative ideas and serious scientific arguments" and that there are "positive racial stereotypes" https://twitter.com/mtaibbi/status/1285304669363933184

Proof:
Sullivan defending racial stereotypes: https://www.currentaffairs.org/2017/04/andrew-sullivan-is-still-racist-after-all-these-years
Sullivan promoting race science as Just The Facts: https://nymag.com/intelligencer/2018/03/denying-genetics-isnt-shutting-down-racism-its-fueling-it.html
Proof that Charles Murray is a racist and Sullivan is using NYMag to lie about it: https://www.currentaffairs.org/2017/07/why-is-charles-murray-odious

You want to defend discussions of race science as legitimate and serious content for New York Magazine? Fine. But be honest about why people object to Sullivan, rather than suggesting that the left is so crazy they can't tolerate a moderate conservative who voted for Obama.