LessWrong is the latter type of site, but this post proposes that it firewall itself from discussions of optimalness entirely and I think that is an overreaction.

You seem to have misread the post. It is 'rational' that is to be distinguished from 'optimal', not the website which is to be firewalled from discussions of optimalness. Eliezer didn't discourage discussions of optimalness (that is, the application of principles of instrumental rationality to specific scenarios). He merely discouraged excessive judgement of people who don't necessarily agree on what is 'optimal' in all situations.