I agree with much of what Smokey wrote but the post and the thread on the micro.blog smacked of one group of people - insiders - deciding for a much larger community.
And what do you say if the person has read this post, considered what you to say, and the response is:
"There's no rule against posting everything I do to the timeline. So I am doing it because it's my mine, and you don't get to tell me how to be."
Community norms are why I have self-hosted on WordPress for nearly 15 years. What happens is that early participants of the community think they can dictate behaviour and expectations to later participants.
They develop a "this is my community, and this is how we behave" mentality, which I find no different than the IRL conversation a white/Christian community have with non-whites/non-Christians who are moving in. The "we don't do that here" conversation.
The disadvantage of community norms is that people stop questioning the purpose of the "norms" and whether they are still relevant for themselves or the community. And this often means that they stop thinking for themselves.
Manton has already spelt out how to behave on his platform. It's his platform, his house, and his house rules. I see nothing in there that excludes posting as often as one wants on any topic one wants so long as his guidelines are met. His instructions are the only norms I care about.