I think there's a balance. Changing your mind when given sufficient reason to do so is bravery. Changing your mind when given inadequate reason to do so is spineless.

But that begs the question: What is adequate reason? curiousllama is saying that many of us will change for inadequate reasons, because we run into someone who knows more than we do on that particular topic. Not who is right, just who knows more. And if we adopt their position, we learn any more, just adopt their position.

So I think that maybe you have to know why they hold that position, and whether that "why" is valid. But if it is, sure, be brave enough to adopt their position. But if you don't know the why, and whether the why is valid, and you adopt their position anyway... that's kind of spineless.