It's 100% a cultural difference. While you see it as personally aggressive and grating, a lot of people see "overly polite" language as a sign that you don't care about the topic being discussed and/or are trying to address an issue politically rather than by merits of a strong argument. Neither of these perceptions is really right or wrong, it just has to do with the perspective you have based on where you grew up and who you've interacted with the most.
From an engineering perspective it'd be optimal if everyone had the same universal expectations for how a conversation should be held, just like how it'd be optimal if everyone spoke the same language. People don't really work that way, though, and just like with languages we try to accommodate each other as much as possible and find middle grounds, etc.