Generally speaking I've noticed that people will listen to someone else just long enough to hear what is being talked about. At that point, one of four basic reactions kicks in:
1) I agree with the speaker
Then I will listen to him for as long as it takes to reinforce my own beliefs.
2) I disagree with the speaker
Then I will dismiss him as a crank of some sort. If I am feeling generous, I may listen just long enough to hear something that I can find fault with.
3) I have no opinion or knowledge on the matter whatsoever
Then I will pay some amount of attention to his speaking style.
3a) If he speaks well and presents himself decently, then I am likely to agree with him.
3b) if he is angry and overblown, or looks cheap or sleazy or ostentatious or self-important, then I am likely to disagree with him.
And that is pretty much the full extent of most peoples' critical listening skills.