Internet commenters are a million times too likely to assume that someone they disagree with is posting in bad faith. This is probably the biggest poison we see on HN, and it's growing. When it comes to minorities of any kind (such as nationality), the effect is to gang up on others and hound them. If that sounds odd, imagine how you'd feel if expressing your personal view on something led people to accuse you of being a spy or a paid agent. That's happening commonly now. For an example from a few months ago, see the thread at https://news.ycombinator.com/item?id=19401961.
This comes from a cognitive bias rather than malice—the bias that, because my views are so obviously bright and light to me, anyone disagreeing must be coming from a dark place—but it's no less poisonous for being unintentional.