The negative reaction to my comment was a bit surprising, considering that citizens of the USA often make similar remarks about their own country, and that these remarks are seen in good light on HN. But it seems that there is a small team of Spanish nationalists around here that will not tolerate such deviations. I do not really care too much about them.
I think this perception is likely affected by cognitive bias, i.e. you noticed some cases of this that stood out for whatever reason, and it formed your perception of HN in general (in this respect). From my perspective, similar remarks about the US are just as much flamebait—even more so, because there are more people who react to comments about the US than about Spain—and we moderate them just as strongly.
I imagine I made the point already, but just to be clear: we need you not to post like the GP comment, not because you owe nationalists better, but because you owe this community better. The container is fragile and we all need to take care of it, so we can keep having a community where interesting things appear. The alternative is scorched earth, which is not interesting.
However, comments where people are criticizing their own background (country, in this case) are more complex and are a special case. I wish I could dig up some of the moderation replies I've posted to commenters in this position over the years, but unfortunately my HN Search fu has failed to find any. (Edit: I did find a small one: https://news.ycombinator.com/item?id=15732812)
They also have a particular taste. As soon as I read this, I could feel that you were probably writing from that perspective. Such comments have a bittersweet quality. Even though the rhetoric is harsh, one can sense that the speaker has 'paid' for it with lived experience. Of course, coming from a minority inside that country, it gets even more complex. But I bet that if someone were to come along and criticize Spain in an ugly and stupid way, you'd be the first to defend it—because you know it and because that would be the only noble thing to do. As John Lennon said to Rolling Stone: I can diss the Beatles, you don't get to diss the Beatles.
However, all this subtlety is lost on the internet. Your comment isn't what it appears to be, but that doesn't matter, because people will react to it as if it is. If you post like this to HN, you will start a flamewar regardless of how much complexity is behind the message, and this will damage the container just the same as someone posting out of ignorance and prejudice. So we need you not to do it here, to protect the community. You're welcome to share your experience in other, more personal and substantive ways, if you choose.
https://news.ycombinator.com/newsguidelines.html
p.s. These are arcane details, but it's interesting to me that https://news.ycombinator.com/item?id=22673470 picked up on the overtones in your comment. Family members (speaking metaphorically) can hear these things.