How about if I write up something on google docs, post a link here, then if there's not much notice in a few days use Discussion for getting initial feedback?

I think that would remove a substantial portion of your potential readers. Just suck it up and post something rough in Discussion, even if it feels uncomfortable.

For example: the piece that starts with "even though altruistic group selection is clearly nonsense" up until the end of the paragraph might be expanded just a little and posted stand-alone in an open thread.
Gather reactions.
Create an expanded post that addresses those reactions.
Post it to Discusssion.
Rinse and repeat.