The internet has always been a place of raging controversy, from the profound to the trivial. I’m not the first to observe that people, at least in our culture, tend to divide fairly equally over many issues. Be it about important issues (like guns or abortion), or about the trivial (like computer games or actors), we rarely agree on anything.
It starts when someone says something and people react. Then more people react to the people reacting (and new people get on board with reacting to what the first person said, starting new waves of reaction). More and more people react to reactions, and the epidemic spreads.
This mind virus was about hurting books, so lots of people had opinions.