re: "What do you have to lose?" - This is simply the very valid argument that many big cities have been Democrat-run for the last 50 or so years, and saying the equivalent of "its not working, stop voting that way".
It doesn't matter what the argument is, it suggests that they are doing very, very poorly. We were discussing whether Trump employed this rhetoric. Yes he did and it was the centerpiece (and nearly totality) of his campaign's black voter outreach. The premise is that conditions for African Americans are a disaster. I'm not sure what there is to dispute here.
All the black folks I know, including myself, did not take it like that. The point, being made in front of an all white audience, as it was, looked a lot more like a reinforcement of the well trodden belief among conservative folks that black people's problems are due to Democratic mismanagement, their own rotten culture, and not racism (because racism hasn't been real since the 60's)