But to be serious, there's endless evidence that it's going on, and if you don't believe it I'm not the one with my head in the sand. (That's a common English idiom meaning "not paying attention," for the foreign state actors out there.)
It's even worse than "not paying attention". It's knowing the truth of the situation and actively avoiding acknowledging it to yourself or anyone else. Hiding your head in the sand and shouting "It's not really happening, it's not really happening!" despite knowing that it is indeed happening.
We – of course – care about manipulation on HN; the only reason this is a site people come to for discussing so many different important topics is that so much effort has gone into ensuring integrity in the content that can be read here. It's just not that easy to engage in astroturfing, shilling, brigading, etc without setting off alarms either in the software or in the many HN users who have finely honed bullshit detectors, because organized, manipulative participation looks and feels so clearly different from earnest participation.