Obviously, there's more than a grain of truth to the view that closed-mindedness is bad. Immunity to new facts and a smug confidence that you couldn't possibly be wrong are serious character flaws and the source of grave mistakes. Yes, of course, dogmatism can be very bad, if the dogma in question is bad. But, as Chesterton teaches, a dogmatic conviction can also be morally praiseworthy and socially valuable. If you doubt that, let us now commence the war on the certainty that murder is wrong, that racism is bad and that a parent's love should be unconditional.
This ultimately is my problem with the anti-certainty chorus; they aren't offended by conviction per se, but by convictions they do not hold. Jean-Paul Sartre famously wrote that "hell is other people." Well, for the new "liberal" champions of skepticism and philosophical humility, hell is the certainty of other people. "Closed-minded" has come to mean "people who disagree with me." (This is a corollary to the popular tendency of defining "diversity" as a bunch of people who look different but think alike). So, for example, pro-lifers have an unshakable "dogmatic" and "faith-based" certainty that abortion is wrong. But, we are told, pro-choicers are merely open-minded and realists. People who are certain gay marriage is good are "enlightened" people, while those whose convictions point elsewhere are zealots.
In other words, certainty has become code among the intellectual priesthood for people and ideas that can be dismissed out of hand. That's what is so offensive about this fashionable nonsense: It breeds the very closed-mindedness it pretends to fight.