I played the clarinet from 4th grade through 8th and quit. I was an average player, didn't really want to practice too much, wanted to do more with my friends and started to feel like band was a little nerdy. I grew up to be a responsible, productive member of society who doesn't quit everything.
That said, whenever I think about it, I regret quitting. I missed out on the marching band, parades, trips - all the really fun parts of band and I wish I had stuck with it.
Both my kids are in band. Both started in 5th grade. I wanted them to try it but the choice was ultimately theirs. DS13 is in his 4th year of band. It's a graded class which he has every day. He had mentioned several times last year that he wanted to quit and I told him that it's not an option. We have a really great music program in our district and I just think that band is good for kids in so many ways.
When he gets discouraged, I tell him:
1. He's got over three years invested in this - keep at it.
2. In another year, it's really going to get fun - football games, marching, trips, friends - a whole lot more than just the band room.
3. Down the road there are scholarship opportunities
4. And band teachers feel free to flame but I lay off the drill about the constant practicing. I ease the pressure a little. He's in class with it every day so I just back off a little.
5. I don't care if he's 1st chair or last, solo or no solo - I just don't want him to miss out on the experience and quit out of frustration.
6. I also spent A LOT of hard-earned money on his sax which he chose to play.
You have to do what you feel is right for your son but I'd push him into sticking it at least until high school.
And I don't think making a kid play an instrument when they don't really want to will turn them against music. There's WAY much great music out there.
Good luck with your decision.