Matt,
I am going to side with you partly, no in the end it might be an empty gesture, but what if? What if someone who is being bullied sees others, school mates and adults, wearing purple today and thinks, maybe I am not alone, or sees someone they know wearing purple and feels comfortable enough to confide in them? What if you make adults aware - like Steve said happened at his work - and they happen to be parents and they talk to their kids about this - to check to be sure they are okay and to be sure they aren't doing it. What if people who might take a stand against it but felt alone and doubted one person could do anything alone, sudden found support in numbers and rallied to help a friend or classmate.
Given how little it takes to do this, or took, vs the potential for good, it is worth the effort even if it reaches only one person. Yes it is not the solution, your post is correct, and sometimes people do the simple stuff, like wear purple, but never show up for the hard stuff - like stepping in to help someone at risk to themselves, but then again, what if?
Andy
PS only 2 of 20 wore purple today - just myself and a fellow gay co-worker. the 4 other gay co-workers didn't know it was happening - sad in a way that it was not better known.