Because he made it our business when he publicly announced it, and later when he publicly stated that it wasn't connected to his prescription drug problem.
If Rush said that it was a private matter, and left it at that, then I wouldn't have anything to say - the man deserves a private life, and he's human like the rest of us. But instead he made public statements that in retrospect make him (and by extension, Rush fans) look rather foolish.
If you're a Rush-basher, own up to it.