I imagine the answer to this question changes based on the age group being polled. However, the Internet hate you see typically comes from males between the ages of 13 and 20. Why? Because Justin Bieber is rich and famous and quasi-talented and can have any pussy he wants on the whole of the planet. Teenage boys do not like this.
"What does Justin Bieber have that I don't? What do girls see in that punk? Why don't millions of chicks scream like they're insane when I walk into a room? FUCK THAT GUY!"