Maybe it's just me but I like to have some type of connection to my teams. I root for all local teams in pro sports and UTSA in college. Sure with technology I could root for and follow teams like the Heat or Alabama closely but what fun would that be?
Agree with what everyone else is saying though, if a t-shirter minds his own business I mind mine. It's when a t-shirter is obnoxious and tries to flaunt a school they never attended that it becomes annoying. Look at
stretch and
benefactor for Exhibit A and B tbh. Both of them are terrible posters that you can tell never attended college.