Yeah, I think the important thing here (and the point of the essay as well) is that whether the content you share is yours or others' should not matter much as long as you provide value to the platform.

This being said, I also understand having some measures against spammers, and so on...

I think HN does a good job of balancing the measures taken against spammers vs. providing a place for you to share your essays. Especially compared to some of the internet communities I've seen or heard so far. As long as you are an active community member who is not here only to promote yourself, sharing your essays occasionally seems to be perfectly ok.