I should maybe clarify that when I say "I see this said all the time" I don't mean specifically the version targeted at internet-rationalists. There's the version aimed at singularitarians (not all internet-rationalists are singularitarians nor vice versa) and a slightly different version claiming that atheism is just another religion, and so forth. The general template is: Thing X is just another religion / just warmed-over Christianity, because here are half a dozen things about it that have some loose resemblance to some religious thing. I find such things uniformly unconvincing; it seems to me that one can draw loose parallels between almost anything and almost anything else.

And: where are the rationalists', or the singularitarians', or the atheists', sacred places? what are their regular religious rituals? what organization corresponds for them to churches and the like? what things are they obliged to believe, as opposed to believing by definition as a member of whatever group? what ancient traditions do they preserve or claim to preserve? Of course you can have a religion without any single one of those things, but the more common features of religion a thing doesn't have the less plausible it is to call it a religion.

I've never seen an argument like this that if applied consistently wouldn't equally assert that many academic disciplines, large companies, political movements, etc., are "religions".