Can obsessing over negative scenarios be sign of depression?

Can be?

Sure. I watch ISIS videos when I'm deep in it.

Everything is viewed negatively when you're depressed, and you feel compelled to expose yourself to things that reinforce that. I do, any way. I'm tempted to say this is a bad thing but I'm not so sure. Sometimes I'll expose myself to something so negative and nasty that it shakes me up a little and changes the trajectory of my thoughts, which can be helpful when you're in in a downward spiral, mood-wise.