It's more so a terrible quote because it is unwise to have a significant emotional attitude towards finding out you're wrong, because this will tend to reinforce irrational defense mechanisms ("Let's agree to disagree!"). The purpose of argument is, I hope, to improve your understanding of the world, so even if you shouldn't be thrilled to find yourself wrong, you shouldn't be afraid of doing so.
It's more so a terrible quote because it is unwise to have a significant emotional attitude towards finding out you're wrong, because this will tend to reinforce irrational defense mechanisms
Yes, it is unwise to have such emotional attitudes, but you don't get rid of them by saying that they are bad. Honestly acknowledging their existence, as in the original quote, is probably a better route to their elimination than an emotionless assertion that losing arguments is good. The quote, on its own, probably doesn't do much good, and perhaps does some harm, but I think it is probably a better step to accomplishing loqi's goal than his phrasing.
A monthly thread for posting rationality-related quotes you've seen recently (or had stored in your quotesfile for ages).