You don't have to read those threads, but polite and measured responses to dumb ideas is one of the best ways to get yourself out of those ideas.

In the example I gave, this clearly didn't apply.

We literally have dumb question threads for exactly that purpose.

There are important details that distinguish the conversations happening in stupid questions threads. These details also cause those threads to not be downvoted.

You want to take a community of people that try to help others understand and instead silence all conversation along lines you disapprove of.

You are throwing out relevant details again and distorting other details in the direction of your argument. The qualifier "all conversation" is inaccurate, for example. Alternatively, if disapproval is taken to be referring to a (value assignment) decision (rather than unreflective emotional response, say), it's tautological that I'd be trying to get rid of things I disapprove of.