If actions that follow from revealed preferences are not welfare maximizing, doesn’t that render the knowledge problem of planned economies null and void?

No. The problem is that without prices, you don’t get information about people’s preferences, including opportunity costs, *at all*. So all the issues with central planning still remain.

Also, it’s not “garbage information” at all, since it still reflects people’s preferences. What the thread is about is essentially that people’s short term preferences might run against their long term preferences sometimes, and similar conflicts. That doesn’t make the information about these preferences wrong, it means *the preferences themselves* are at odds with each other.

Obviously this is very normal. We as a society can think of whether that’s worthwhile a heavy handed intervention. We still ban asbestos even if some people might still use it fully aware of the dangers, simply because it’s cheap for example. We don’t ban doughnuts even if we know that sugary food is generally unhealthy and might go against the “long term preference” of people to be healthy because we don’t see the curtailing of our rights to be worth the benefit in this case. So we don’t necessarily even want some strict adherence to what’s “best” and people most likely wouldn’t be particularly fond of some central planner with a Draconian adherence to whatever they deem to be “welfare maximizing”.

And lastly, to reiterate, without prices revealing preferences, you wouldn’t know them period.