Am I supposed to know who he is?

exactly. And that's why they immediately go to "oh, you think both sides are equally bad?" when nobody says that.

Because either you accept the Democratic centrist position and vote for them, or to them you've equated the two.

The Democrats can be better than Trump, and still unacceptable to support. Not just as a moral matter, but as a tactical one as well. Because as long as Schumer and Biden style neoliberalism is a going concern and in leadership, progressives (much less socialists) are not only going to be shutted aside, but actively opposed, as we've seen since 2016.