What prevents the user from selecting a different video and who is the arbiter of 'what makes sense and what doesn't?'

I suppose those can be rhetorical questions, if you want. To be clear, I suspect I hold very extreme views on the concept of free speech, at least from your perspective. Lest you read too much into that, the speech I'm defending sometimes comes from people who would harm me simply by virtue of my not being white.

In this case, the lady is a journalist. Her reporting included extremist videos. You're saying YouTube is not the place to share investigative journalism because it's highly destructive hate speech.