Cliff notes
-People don't like his pro drug stance
-People hate his shitty music
-People hate the fact that he still milks his victory over Royler
-People hate that he bashes gi grappling
-People hate that he thinks he invented a "system" of grappling that is different then BJJ, even though BJJ encompasses all of the moves he uses.
-People hate how he claims his system is a revolution, and that professors don't teach it because they are scared their students will start beating them.
-People hate his marketing
-Many of his follows are fanboi tools who think he is god
-People hate how he makes up goofy names for moves
-People hate how many moves in his system are attribute dependent (insane flexibility)
-People don't think his school is worthy of all the hype it gets. They don't have particularly good competition records
-10th planet fans always point out how they have a few great grapplers (sotiropoulos,etc). All his top guys were studs with tons of experience before joining 10th planet.
-People hate how he affiliates with Ari Bolden, who is the BJJ laughing stock fraud of the internet.
-People hate how he affiliated with another fraud, Brandon Quick, although he kicked him out when he found out.
That should give you some ideas to get started.