I don't understand the issue. I don't like loud blaring music on the course either, but I have never heard it at the levels you guys are describing. I've only heard it in passing. I am guessing its not as if the music guy is just randomly following you around the course with his music always in earshot, is it?
I wouldn't call you a control freak, but I also wouldn't say you are being overly polite. Don't confuse "Not Rude" with "Overly Polite". Because you would be rude for asking someone else to turn off their music in a public park. If it really is at obnoxious levels that bother you so much, you can always call the police and let them deal with it.
If he's playing in the group behind you, he quite literally is following you around the course.
I'm sure there is a disconnect amongst the folks here as to what exactly (too) "loud" is. For some, it is "loud" if they can hear it from more than 5-10 feet away. For others, "loud" is only if you can still hear it from 50-100+ yards away. Doubt we'll get agreement on that definition, ever.
I posted before that my philosophy is no one likes your music so keep it to yourself. I don't want to inflict my musical tastes on others, so I generally expect the same courtesy in return. That said, if people insist on listening to music, so be it so long as it is reasonably contained.
If I walk up to a group and don't realize the music is playing until I'm standing with them, I've got no issue really. I'd probably prefer it be turned off while I'm there but if I'm moving right through (or they are), I'll tolerate it for a few moments rather than make a big deal about it.
But if someone is playing music and I can hear it from 100+ feet away, IMO, it's too loud. That, to me, isn't just about them enjoying their music. That is about them wanting everyone, whether they want to or not, to "enjoy" their music. I feel that way whether we're talking about music on the course, in your car in traffic, or in your own home.