The only thing wrong with it is that you generally have to have a Facebook account to read Facebook content, which means you have to give them your real name. It appears that this month Facebook is allowing people to read this particular post, but they aggressively put the sign up wall wherever they thing it will generate the most conversions. You certainly can not see John Carmack's past posts without a Facebook account. Facebook is not the open web.
Technically you can violate the ToS and set up a fake account, but that's a bit of an inconvenience
Whether or not a post is available to "the public" (signed in or not) is completely the choice of the author, not some mysterious committee at Facebook.
Have you tried to read a page on facebook without an account? It's intended to be an almost unusable experience.
On loading a page, I get a modal popup obscuring all content insisting I "register" or "login", with a "not now" option. Then when you click "not now", the bottom third of the screen is obscured by a fixed overlay.
It is loosely describable as readable, but in practice, it's a fight to read it. The element has randomly generated id, so can't easily be blocked with ublock or similar.
I agree Facebook is a bad place for placing public content. Note though that it's currently a lot more bearable if you disable JavaScript for Facebook. As someone who doesn't use Facebook at all it's easy for me to keep it disabled with NoScript. Then I just see content, no popups.
And what happens when facebook decides otherwise? Because it seems they already have with their strategy of curating content and information to maximise engagement.
Technically you can violate the ToS and set up a fake account, but that's a bit of an inconvenience