He is basically complaining about my posts being off-topic in my own thread. I made the thread, I get to decide what its about -- he doesn't. Pretty ironic that this is coming from a guy who considers himself to be such an astute champion of free speech. He could just move on, but instead he would rather post about how unfair the rules are in his Meta LiveJournal.
That is clearly false. We have had posts of our own deleted from our own threads. (wrongly in our own case ). Sometimes as a direct response to questions or accusations that are left there that are clearly more off topic.
However, of course you can go off topic in your own thread if they hold you to the rules as theymos has explained them. Every post should be relevant directly to the OP at least in some part of your post if not the majority of it.
So yes you can certainly be off topic in your own thread if they want to claim you are.
I would say the only context you can not be off topic at all if is they allow your thread to be derailed even after you report the offending posts and you just go with the new permitted flow the mods are permitting even after you complain. Then to moderate it would be clear moderator abuse.
I would say in most cases the thread starter should be allowed some free reign but to let it go to extremes would of course waste other contributors effort and time addressing the original point if you were to then just veer off on a totally unrelated tangent.
Permitted flow is complex and needs to really be thrashed out and detailed guidelines brought in.
The mods really (although sometimes taking the piss imho) are left to guess what is and what is not permitted flow, so really there will be some variance in decisions taken. We do have some small sympathy for getting moderation 100% spot on because that is at this time impossible.