The discomfort is partly because you can make yourself like or hate people you don't know personally and trying to come up with bad/good things to say about them is one approach how to do it. You start process insulting them and you can see yourself starting to feel differently and some might feel good about the process and where it leads.
You know how people close themselves into bubbles that says only bad things about some outside group and then become to genuinely hate that outside group? It is the same, but is small scale, temporary limited and easier to detect.