Stack Overflow is CC licensed

> Content contributed before 2011-04-08 (UTC) is distributed under the terms of CC BY-SA 2.5. Content contributed from 2011-04-08 up to but not including 2018-05-02 (UTC) is distributed under the terms of CC BY-SA 3.0. Content contributed on or after 2018-05-02 (UTC) is distributed under the terms of CC BY-SA 4.0.

True for OP and true for Linus Torvalds. Is the solution to stop with open source, and never to publish anything? ;)

They were publicly posting to a search-indexed website with the intent of helping people. I may be wrong, but I’m pretty sure that they understood that SO owned the messages and were already profiting off of them.