It's not "incoherent" at all and by using that label, you're falling into the same trap as JM using the label "ostrich mentality".

Imagine a political science professor that lived and breathed "politics" all the time such that he teaches classrooms, writes books, and sits on panels debating various policies with others. Now, imagine a friend's mother invites him to Thanksgiving dinner. It is suggested that politics not be discussed. Yes, the professor could be impossibly obstinate about it and say, "that's delusional -- there are politics in the production of that turkey, the food lobby, the creation of the Federal Holidays, etc. Politics is embedded in _everything_!"

However, the professor doesn't have to be that inflexible. He can avoid politics talk during that dinner and the very next day, sit on a panel with Noam Chomsky and Christopher Hitchens and debate every political hot button topic under the sun.

Turning off-and-on the political discourse switch for certain venues is not "ostrich mentality" nor "incoherent". Perhaps there's a different reason that some people don't want politics on HN: the political comments are low quality.

Likewise, the mother isn't delusional/incoherent in thinking that politics doesn't exist everywhere. She's just attempting to set the tone for a pleasant agreeable evening.