Why do white men go trolling on youtube videos such as why black girls, asian girls prefer white guys?

Whitey people are inferior. They have no brain and are very insecure. So, as you could understand, it makes them happy when poc ever like them back. When it doesn't happen (most of the time,) they just start ranting and glorifying their little whitey female monsters. However, when the very few poc women who acknowledge their existence reciprocate them, they feel the need to boast about it. Try to understand them. It's unusual for them, so they want everybody to know a poc woman has ever preferred them over real men.