It's quite simple: if you dislike a composer, they're a plagiarist. If you like them, they have a distinctive style.
Aptly put Mr. Bond. The tale of the double standard is proliferated throughout this forum.
But I think we all must concede that Horner copies himself more than any other composer working in the industry at this time. Even people who have limited musical training can pick out bits from his other films. That's really not a good sign.
Horner's problem is that he makes no attempt to HIDE the reuse of his own material. I played Troy for a friend of mine, and he got sick of hearing the danger theme played ad nauseum, with no variation or change. Just the same 4 notes over and over, played on nearly every chord change in the action music.