I'd say you were entirely wrong. Crass had no specific political message at all - indeed, went out of their way to avoid being aligned with any political group. They dealt with issues and causes, often in a very abstract way, without allying themselves, ever.
Isn't this pretty much what the Clash and the Dead Kennedys did?
Strikes me you have a very narrow view of what constitutes politics
As for the middle class thing - i'm not sensitive about it at all, it's just lazy and wrong. Not all of Crass were middle-class, so it's facile to use that as a stick to beat them with. Simple, really