Mainly that he's not a Marxist, a rad-lib at best. Gives words which are cheap to anti-capitalism but doesn't give solidarity to targets of US imperialist attack unless convenient and costless (Cuba and Palestine at this point, he's in the Russia-bad camp, against China, etc).
I admit he could be amusing but I hope no one here falls for him as anything but window dressing himself on the US political system, the uh far left end of what is permissible in the mainstream which isn't that left at all as I mentioned, no actually risky solidarity (China, DPRK, Russia), no real solutions beyond platitudes about loving your neighbor and brother this, sister that preacher bullshit speaking. Oh he desires for change and probably wishes he could put together an MLK like coalition but doesn't realize as liberals do not that if the USSR hadn't been there banging on about the civil rights and humiliating the US in front of non-aligned states they would have killed MLK a lot sooner and a lot of his followers too rather than compromising for face.
There are many levels of traps and false paths in the US system designed to capture people and prevent them from reaching Marxism. We in no way have to hand it to anyone who is not either a principled Marxist or with us in a principled anti-imperialist stance that they maintain at great cost. He is neither, never has been. Celebrated the fall of the USSR, etc.
Being so fucking glib about which monstrous arm runs the evil machine of torture, horror, pain, suffering, death, and agony unto all humankind.
It's like a trolley problem where one track kills orphans, the other also kills orphans but leaves in its wake among the bodies pride flags and #democracy posters so it's better somehow to you indoctrinated westerners.