I wouldn't feel bad about not wanting to tank. Sure if you ran a tank up to 50 if might be easier for you to get into ops or faster ques using the group finder sometimes but it seems like your guild has a pretty strong raiding group from what you have said.
Everyone clings to that one professions that they like more then other professions. My first character is a jedi sentinel but after trying the jedi shadow and running him as a tank i find that im on my shadow tank 95% of the time now
then my main character that is the sentinel dps. So dont worry about it.