Marching Band is like anything else in life. It's not for everybody. On the other hand, it can be a great experience. You get out of it what you put into it.
As for me, I did four years of High School marching band followed by four years of college marching band. I know I'm probably never going to be performing with the L.A. Phil, but I enjoy playing my trumpet and I'm grateful for all the experiences marching band has given me. Not only did I have numerous opportunities to play and perform, but being in the marching band also taught me how to conduct, arrange, compose, and lead a musical ensemble.
Marching Band worked for me. It doesn't work for everyone. Simple as that.