Certainly I understand that HAVING a registry does not equal ANNOUNCING the registry -- that would ALWAYS be a no-no. We are discussing simply having a registry for something like a housewarming, and only telling people about it if they ask.
I don't think anyone said it is RUDE to have a housewarming registry. And I certainly think that we'd all agree that there is nothing wrong with telling your relatives and close friends who might be asked by others for ideas a few things you would like, as long as they (and you) wait until asked.
But setting up a registry for yourself when you move, graduate, have a birthday, Christmas, bar/bat mitzvah, etc., even though these are events for which people buy gifts, strikes many of us here as really off-putting, even if you don't send the registry info out. It may not be an etiquette violation, but you can't control how people will feel about it, and that's what we are telling the OP. People may get used to such registries, as they have, in my lifetime, to baby registries, which seemed odd at first. But they haven't yet.
In my opinion, it just seems too anticipatory of others' generosity and too much an attempt to influence the form that generosity should take.
I appreciate that the same logic applies to wedding registries. The reason wedding registries are acceptable is that they were originally only for things that come in patterns or sets, so that's the only way guests could buy them; the store kept track of the pattern and the number that had already been purchased. (And that's why I have the same objection to wedding registries that go on and on for page after page, way past things that come in patterns or sets, too. They make me feel much more pushed to choose my gift only from the preselected items. The whole term "off-registry," as if it were a departure from the expected norm, makes me cringe.)