I agree it's not that uncommon to see stuff flagged and removed, especially of political nature, especially when it's something not viewed in a positive light by the moderators in HN. It's not exactly 'free speech guaranteed' on HN.

From guidelines: "Off-Topic: Most stories about politics, or crime, or sports, unless they're evidence of some interesting new phenomenon. Videos of pratfalls or disasters, or cute animal pictures. If they'd cover it on TV news, it's probably off-topic."

This allows them a lot of leeway to take stuff down.