I personally like Glocks because I think they're king when reliability is key.
Reasons for Glock hate that come to mind:
They have polymer components. "omg guns shudnt be plastic!..."
The grip is relatively large. Can be unwieldy for people with small hands.
The rise of the Glock is perceived as a threat to 1911 fan boys.
They have several safeties, but none are of the conventional type that allow the user to essentially "turn the gun off." This can prove to be problematic for certified dip****s.
Glocks are associated with thug culture.
Glocks are also associated with cops.
My only real gripe with the Glock is the terrible trigger. I'm in the process of looking for a good trigger upgrade now.
I'm sure I missed a bunch of stuff that the real Glock haters will be happy to fill us in on.