for me this becomes a really simple issue,
1. Every one who responded to this with "Screw your guild" " your guild sucks" " to hell with those guys" or anything similar to that, is a part of the reason that the WoW player base has a shit reputation for being anti-social trolls, and asses.
Is it completely fine to play however you want? Absolutely, is it fine to play however you want and expect others to accept it? Hell no, You made a choice, now You live with the results. if the group you are in doesn't approve of that choice then it's your job to find a compromise or respectfully part ways like adults, not throw a temper tantrum and pick up your metaphorical basket ball and go home.
2 As a raider you are a part of your team, and if it's a casual raid then it's likely that when the leader is looking at how well someone is doing he is more concerned with where that player falls on a scale of personal potential. So if you have a hunter that is just not very good, but they are trying as hard as they can, and attempting to improve that is fine, where if you have a lock like you who is doing more damage than the hunter, but is admittedly under-preforming based on personal potential, that is a slap in the face to the whole raid, because there are people who are doing all they can to progress and you are sitting back and coasting. In this situation I think it's more a matter of you refusing to put in the effort rather than you dps or spec, had you switched and shown that your gain isn't significant or if it was, and you spoke with the raid lead and agreed to play the more optimal spec when asked but could fall back to your proffered spec when the added DPS was not important, I doubt this would have been an issue.
3. People need to take the whole it's my 15 dollars stuff and shove it directly you know where, because that is a pathetic argument, because it may be your 15 dollars but the second you are in a group you are simply 1 person in the group, exactly no more or less important than any other person in it. they all payed their 15 dollars, so your desires are not one spec more important than theirs. If you have a way you like to play great, find people that feel the same way, or a place where you playing that was doesn't bother others. In short be decent human beings for christ's sake.