> there are obvious shared talking points that come in waves.

Groups of people who wake up at the same time of the day often have a tendency to be from a similar place, hold similar values and consume similar media.

Just because a bunch of people came to the same conclusion and have had their opinions coalesce around some common ideas, doesn't mean it's astroturfing. There's a noticeable difference between the opinions of HN USA and HN EU as the timezones shift.