I quite honestly think that a big part of the problem people have with him is that he's "visible".
Trans men have for a long time been able to slip under the proverbial radar.
When people say "transsexuals" they usually mean trans women, because trans men go unnoticed.
Chaz Bono's open and public transition has meant people are aware of the existence of trans men more than before.
This makes people uncomfortable because they don't want to be seen as "trans" because of the public reaction they fear and because of their own disliking of "trans" and what they themselves connect that to.
Some trans people are the most transphobic people I know.
In part I believe this is a form of self preservation (they feel that if they rag on trans people then people won't know they're trans themselves) but I think a bigger part of this is a form of self hatred (hating that they are trans, that they had to transition to be themselves, that society won't accept 'em, etc, etc, etc.)
Those things together I think are the primary reason why some trans guys dislike Chaz.
Honestly, they should dislike me too then, because I'm openly trans and publicly speak out as a trans man for trans rights, both legal and social.