Since Rob seems to object to the ban (a view I'd urge him to reconsider) and in order to have the best of both worlds, I strongly believe that the ability to mute selected threads should be made available to members.
The technology doesn't exist.
I mean, I literally asked about this years ago, thoroughly sick of having One Word Posts or some similarly inane thread appear in the 'new replies to your posts' list. But the technology that the forum runs on doesn't have this option. Once you've posted on a thread it will show up there (even if you delete the post).
And of course 'show unread posts' will show all threads whether you've posted on them or not.
But the fact remains, members are not obliged to read these threads. They are certainly not obliged to participate in them. Everyone who participates in political threads has decided to do so. Yes, that might be because various bits of their lower primal brain have been triggered, but people have to make choices about these things, and can teach themselves to stop participating even if they started.
I maintain the view that people who are participating in the political threads more than the music ones are doing so simply because they find politics more 'interesting' in some way that music. If you didn't have the political threads here on GMG as an option, I am not convinced that this would somehow cause them to be less interested in politics and more interested in music, it would just mean that they engaged their interest in politics somewhere other than GMG.
Would it insulate GMG from drama? Yes. Would the result be fewer people leaving GMG? Again I'm not that convinced. It would perhaps just mean more people leaving quietly and fewer people doing the drama queen flame-out of deleting their accounts (an action that seems way, way more popular on GMG than I've ever seen anywhere else). You might not notice them leaving, but I reckon a lot of them would still be effectively leaving, spending their time being engaged in political discussion wherever that was occurring.
If you want more activity in the classical threads, the solution is not to stop people talking about other things, the solution is to make the classical threads more interesting.