Oh...tough decision. I often ask myself the same question, although mine is a what if because my son is only 24 months. I guess I ask myself that question because I want to be prepared if my son wanted to do something other than "traditional" boy sports. I would want to say "Yes, go for it!" I would want to tell family and other people "Why do you care? It's awesome that he is doing something he likes." I would also want to let my son know that it is fun to do something different and that he doesn't have to play football or soccer because everyone else does.
The things I imagine my son being interested in are ballet (men are such beautiful dancers) and show jumping. I would receive a lot of grief from family if this ever happened but oh well!
And, if your son is really good at cheer leading, then he could go to A&M and be a yell leader :-) Can you tell I'm an Aggie????
Also, male cheer leaders get to hang out with all the girl cheer leaders, they are usually handsome and very athletic looking (we had some at one of my high schools.
Good luck! Please let us know what you choose.