I, by no means, approve of the REACT Copyright. However, many people are not understanding why they're doing it. The Fine Bros REACT on videos that don't belong to them, making them susceptible to copyright claims. I wouldn't expect The Fine Bros to be total jerks about it, though. I don't know them personally, of course, but they're not the only Class-A YouTuber that does reaction videos. So to be jerks about it is to surely ruin them. In all honesty, it's likely personal security rather than a malicious, advantageous move.