Negativity gets more clicks. When you say something like "I love Marvel" in a youtube video, you're gonna get drowned out by a sea of people who have similar opinions.
But when you say "I hate Marvel", it sticks out beacuse not as many have that opinion, but also because people will be curious to hear what you didnt like about it.
I'm not saying that there's more to dislike than like in Marvel movies, it's just that exaggerated, unpopular opinions get more traction. So from a process similar to natural selection, the opinions that get the most views result in more similar videos being made.
As for your friend, they sounds like me from 2 years ago lol. They'll eventually learn to be comfortable with their own opinion to not enforce it as being "correct".