This is a non-profit youth center. What's of paramount importance in this case isn't what hurts and doesn't hurt a business. It's what hurts and doesn't hurt the young people that come to Rocketown so that they have a safe place to go after school or on the weekends and an anti-gay agenda DOES hurt those kids.
Although this is somewhat different, Ill say it anyway. I went to a private catholic university. We were required to take 3 religion courses that relied heavily on bible reading and in some cases going to mass. Did I go into the dean's office and say "fuck you! Satan lives! I'm not taking this bullshit!" No, because I'm not an arrogant prick. I sucked it up, did my work and got through them.
This kid should have done the same if his job was important to him. You aren't going to change the opinion of these people, this youth center or entire swaths of Christians by wearing a fucking pop punk t-shirt. If he wants to make a difference he should be working for a party or candidate that will fight for equality.
Also, again, why was he working there?