ISTM we should encourage a default norm of respect for people who change their minds on serious topics, even if we disagree with the switch or the reasoning (within bounds). Yes, this norm could be gamed if it goes too far, but right now the norm is that changing one's mind is an admission of weakness, and that depresses the sanity waterline considerably.

ETA: Sorry for the ambiguity— as you guys point out, we already do this regularly on LW. It's in real life that this needs to start happening.