Joss Whedon
Before I saw any of Whedon's shows, when my only exposure to him was his run on the Astonishing X-Men comics (which didn't do much for me), I used to be really bothered and get defensive of him when I read some of the harsher feminist criticisms - not because I had any reason to think Joss Whedon was particularly bad or good at feminism, but because the nature and tone of the criticisms bothered me.
Yet once I actually became a fan of first Firefly and then Buffy, and concluded that Joss Whedon is a genius at television storytelling, I became quickly much more bothered by the Joss-is-my-master-he-can-do-no-wrong people (who I had been aware of before, but hadn't spared much thought or been bothered by). I think these days I've found a more happy medium between Whedon's critics and his supporters - but it still seems weird to me that becoming a fan of the guy led me to be more negative about his fans than I had been prior to being a fan of his work.
Yet once I actually became a fan of first Firefly and then Buffy, and concluded that Joss Whedon is a genius at television storytelling, I became quickly much more bothered by the Joss-is-my-master-he-can-do-no-wrong people (who I had been aware of before, but hadn't spared much thought or been bothered by). I think these days I've found a more happy medium between Whedon's critics and his supporters - but it still seems weird to me that becoming a fan of the guy led me to be more negative about his fans than I had been prior to being a fan of his work.