I’m not sure we can make those assumptions. Back in the day of the rise of Howard Stern, there were reports that showed his haters would listen for longer stretches of time than his fans. I cannot speculate as to why that is, nor can I speculate why racist trolls are watching any given YouTube video, or if they’re even watching or, as you surmise, are just trolling without watching. I imagine it is a mix, not strictly one way or the other.
People who hate something can still be entranced by it or engage with it. Jon Stewart and his writing staff must have watched 10,000 hours of Fox News over the course of his Daily Show career so that he could generate counterpoints, a form of engagement. Certainly, there are wannabe anti-Jon Stewarts out there, perusing the mainstream media, looking for ways to make counterpoints.
I recall my own mother yelling at the television when I was a child anytime a politician she didn’t like was giving a speech.
And, these days, a friend of mine who is a person of color pretty far to the left on the political spectrum spends inordinate amounts of time reading alt-right sites to see what it is they’re up to, to understand how they have gained momentum, and what implications the alt-right has for his own life and future. Some of it comes from boredom, but some of it comes from curiosity or fascination.
I agree with the premise that a high percentage of racist white middle-Americans are not reading feminist New York Times Op-Eds, but the number is more than zero, and my suspicion is it’s higher than we would intuitively guess.