For the vast majority of my career I have been one of those anti-marching band guy. I felt that marching band didn't place value on many important aspects of music such as intonation, balance, tone quality, and phrasing. Additionally I felt that too much value was being placed on  non musical things such as marching, competition, and a general "sports" mentality where winning a big trophy was more important than the beauty and power of the music. 
This disdain for marching band stemmed from my early musical study in high school. I grew up in South Carolina, a state that is dominated by marching band. We would practice four days a week, football on Friday night, and a competition on Saturday. Concert band was an afterthought. We never worked on intonation, balance, tone quality, articulation, or phrasing, nor was I ever exposed to musicians, or musical ensembles, that did not perform on a football field. When it came time for Concert Band Contest my band director would pass out easy music so we could guarantee a "superior" rating, and yes - get a big trophy.
I knew early on I wanted to go in to music as a career. I felt that this culture of placing more emphasis on making shapes on a football field than the beauty of music was useless. I left my high school and went of to the North Caroling School of the Arts. 
Later in my life my my attitude towards marching band shifted. This first occurred when I was on the  staff at Lassiter High School north of Atlanta. Lassiter had one of the finest marching bands in the country. The year I worked there, 1997, they won Bands of America. What the also had was the finest high school wind ensemble I'd ever heard. Many people from that program have gone on to become professional musicians including Chris Martin, the Principal Trumpet of the Chicago Symphony. 
How is this possible? How can a program which places such an emphasis on marching band still have a great concert band? Then I heard something that changed my perception. I heard the marching band warming up on the first day of band camp...on Bach Chorals, and they sounded fantastic. I then realized that Lassiter didn't have a great marching band, and a great concert band; they had a great band program that emphasized intonation, tone quality, balance, and phrasing. They brought those values to the concert hall, or the football field, or anywhere else 
This was later emphasized for me when I returned to South Carolina as a collegiate band director. Wando High School in Charleston had won the State Marching Band Competition something insane like seven years in a row. It drove the other high school band directors insane. They'd buy new uniforms and Wando would still beat them. They'd schedule more marching band practice time and Wando would still beat them. They'd amp up their intensity and demand the same from the students AND WANDO WOULD STILL WIN! Finally the idea was floated that Wando not be allowed to compete for awhile. They couldn't be defeated. What no one seemed to notice was that Wando had the finest concert band in the state, as well as the finest jazz band. All of their students were encouraged to take private lessons. They emphasized intonation, tone quality, balance, and phrasing. 
The lesson I learned is that music is music. It doesn't matter if it's a symphony orchestra, marching band, punk band, show choir, musical theater, opera, or anything else. Intonation, tone quality, balance, phrasing, and musical sincerity is what will make to great. The problem is we get distracted by marching, or costumes, or volume, or any number of things that keep us from improving as musicians. Can marching band be done musically? Absolutely. Is it being done musically? Sadly not usually. My hope is that as drum corps place more and more emphasis on the musical aspects this will hopefully trickle down to the high schools. Don't think drum corps emphasize these values? Watch Carolina Crown warm up:

  https://www.youtube.com/watch?v=lEL1Sc7K4DY

And guess what? They won last year.