Being the type of person who analyzes thins all the time, chances are if I express an opinion, it is because I put a lot of thought into it. When I engage in conversation with someone, it is from the perspective of analyzing the new information that they can give me, the different perspective.
When someone approaches a conversation about ideas from the perspective of trying to be polite or aggreable, it's like we're trying to have different conversations.
Moreover, people are so willing to make bold statements based on vague impressions ans prejudices. Since one tends to assume that other people are the same as them, unless presented with dramatic and specific evidence to the contrary, I interpret these proclamations as if they have gone through the same rigorous vetting that such as statement from me would have gone through.
Humans are weird.