Oh, Salem.
What you're saying, then, is that any ignorant, rude, offending, misled, or otherwise generally unacceptable comment we come across should be ignored, unless the person in question actively states that he would like others to present their views and argue with/correct him.
Unfortunately, it just doesn't work like that. Firstly, if someone makes such an outrageous statement such as "x people are better than y people", they are opening themselves up to attack/argument. People will disagree, and they have just as much right to present their argument as the original person did to present their views. One cannot simply waltz around spouting their opinions and thoughts, and expect everyone to listen yet not to combat them.
Secondly, arguing ideas can help to reinforce, develop, and expand them. It's all part of progress and evolution. Arguing and debating makes you think, and being made to rethink and re-evaluate your ideas is a Good Thing. It can either a) build and strengthen the foundations of your ideas and help you to defend them adequately (which is practically essential if they're views such as the example I gave up above), or b) make you see the flaws in your logic, and allow you to adopt new and better ideas instead. Can you honestly say that never having your ideas or thoughts contested unless you allow them to be is good?
In my experience, the ones who find it "rude" or "offending" when I find flaws in their logic and attempt to present an alternative point of view, are the ones who simply refuse to open their minds and think outside their little "safety shell", because they are scared to think differently, scared that the other person may be right, and scared that their perfect little utopian illusion of a world that they cling to may suddenly shatter in the presence of logic and common sense.
--Arquin