Because thats disrespecting the opinion of the person you're contradicting. Even if you see their opinions as invalid, they see their opinions as correct and you have to accept that.
Ok, but you see I'm not going to hate you for having these opinions because these are YOUR opinions. The fact that these are your opinion make it that this is what you believe and people can't change what you believe. People can disagree with your opinion which can be frustrating because people aren't seeing things from your prospective and you want them to see how you think. However, when you start to hate someone because they have different beliefs than you is when it starts to become an issue. And when you dedicate entire streams to contradict what this person's belief is and what that person's belief is, its just going to cause problems and make you hate each other even more.