They hate him because he left the Lakers.
They think he sucks because they think his year on the Lakers is who he is as a player.
I don't think any real Laker fan actually thinks he sucks, they just had unrealistic expectations from him last season. But yes, they definitely hate him for leaving their team. Which I really don't understand because all I heard from Laker fans last season was constant complaints about him...
The complaints were because he was crying way too much on the court. Dwight is the only player i seen yelling at Steve Nash, Steve Nash!!! Not mad he left, didn't like his attitude. I get a kick out of seeing his reaction to Harden's lazy defense.
Dwight hasn't gotten out the first round since 2011, although he didn't play in 2012 playoffs. Still 2011 and 2013 record 2-8.