Sure, everyone and every group has a de facto agenda. But the agenda of HN feels to me like "have productive, civil discourse, in a generally pro-technological advancement vein". The agenda of, say, /pol/, is much more directional and polarized (propagating racist and fascist memes, basically, with the broader goal of propagating racism and fascism). There's a much tighter focus and intent to the latter, which makes it feel much more like "an agenda" colloquially, and it seems like a distinction worth noting, rather than eliding it by saying "everyone has an agenda."