What is something you used to believe, preferably something concrete with direct or implied predictions, that you now know was dead wrong. Was your belief rational given what you knew and could know back then, or was it irrational, and why?
Edit: I feel like some of these are getting a bit glib and political. Please try to explain what false assumptions or biases were underlying your beliefs - be introspective - this is LW after all.
Well, there are some relevant facts, such as whether children raised by gay couples end up less well-adjusted than those raised by straight couples.
Presumably what you mean is whether children raised by gay couples end up less well-adjusted than they would if they weren't raised by gay couples, right?
I mean, to pick an extreme case for clarity: if it turned out that gay couples only ever raised children who would never have been raised by straight couples even if there were no gay couples, then I don't see how the fact you cite is relevant to gay marriage.