I understand that there are people don't care at all about FOSS. However, I assume that people in here have an interest to use FOSS over a closed source program. The degree of priority varies by people.
If you are know that Stack Exchange is not open sourced, then why do you still participate here and contribute content to it?
I admit online services that run on nonfree code are not ideal, under the FSF's philosophy. However, even the FSF says that services designed primarily to publish information to users does not cause the problems inherent in letting a remote service run software for you:
The original idea of web servers wasn't to do computing for you, a visitor; it was to publish information for you to access. Even today this is what most web sites do, and it doesn't raise the SaaSS issue, because accessing someone's published information on a web site isn't a matter of your own computing. Neither is use of a blog site to publish your own works, or using a microblogging service such as Mastodon, or StatusNet, or Ex-Twitter. (These services may or may not have other problems, depending on details.) The same goes for other communication not meant to be private, such as chat groups.
In this article, they highlight the danger of letting someone else do your "computing," which they define as something you could do on your own hardware if you had the code to do so. But uploading and displaying a collective of user-submitted material is categorically not something that can be done on an individual basis, so the article indicates this is not a problematic case for remote computing.
Even if Stack Exchange suddenly released all their code under the GPL tomorrow, this wouldn't change things much for me! It would make it marginally easier to run a competing service, but other free Q&A implementations already exist. The main factor keeping me on Stack Exchange is social weight (i.e., everyone else and their Q&A text is already here), not the absence of competing services. The code to make a Q&A site is not particularly hard; operational concerns such as moderation, uptime, user activity, advertising policies, and licensing of posts are of vastly greater importance to me than the straightforward code that uploads and displays the site's public content. So far, I have encountered no other site that outweighs SE, on the whole, in these collection of factors.
As someone who cares about digital freedoms, I find it much more valuable that they require all user-submitted questions and answers to be available under Creative Commons licenses. To me, this is a vastly greater freedom (and one not widely admitted elsewhere online, outside of Wikipedia) than merely releasing the code of a Q&A website.
When I interact with SE, I do so using free software running on a free OS, exchanging free content. Nothing SE does requires or pressurises me not to use free software.
As far as I can tell, your question presumes that it is desirable that nobody should use non-free software, because otherwise there's no issue with using free software to put free content onto a distribution platform using free formats, but run by non-free software. But nobody I know of in the free software community holds the position that the whole world must stop using non-free software; the position is always that (a) I should not use it, and (b) other people should not, by their software choices, require or encourage me to use it.
Consider RMS's famous piece about Word attachments. He notes that
For us users of free operating systems, receiving Word documents is an inconvenience or an obstacle. But the worst impact of sending Word format is on people who might switch to free systems
At no point does he say that the choice to use Word to write an attachment is bad for the person who chooses to use it. He goes on to note that
I therefore make a practice of responding to Word attachments with a polite message explaining why the practice of sending Word files is a bad thing, and asking the person to resend the material in a nonsecret format.
Note that he doesn't suggest they stop using Word; only that they use it in such a way that he doesn't experience any pressure to run Word. His new standard, canned response specifically tells them how to send "plain text, HTML or PDF using Word". That somebody else uses Word to write, say, ASCII attachments is completely fine with rms. I've no doubt he wishes they would freely choose to use emacs to do that instead, but he doesn't go so far as to say there is any reason why they should so choose, if they don't wish to.
So in brief, I take no exception to what SE is doing with respect to the freedom of their backend code because, in that respect, they are doing nothing that is exceptionable by the normal standards of the free software community. (That sentence is quite carefully worded because I take a number of other exceptions to what SE does; just that none of them relate to the freedom of the backend code.)
Regarding the specific mention of codidact, I'd love to use it, but however free its backend may be, it doesn't have an Open-Source-specific "community" (using that term the way codidact does, to mean a topic-specific site subsection). So I simply can't have there the interactions that I have here.
I checked their server version with a manual http request already about in 2010, and I have seen that they are a 100% Microsoft-ish, closed source, Windows server, dotnet company. On this reason, I did not plan to register here et al.
First another, paid Q&A site always appeared in the Google search, it was maybe called experts exchange or so. I disliked them, they had all the negative side of the SE, but they also wanted money for the right of contributing by them. That was hilarious, and how they poisoned the Google algorithm, was yet worse. As far I know, the SE was born partially as their antitheses.
However, I knew that they automatically give moderation privileges, which is very unusual - typically, moderation-related things, i.e. having a word in topicality, having a freedom to fight misuses - is reserved for a close circle, selected on personal sympathy. That is how internet and such virtual power works in the internet communities, leaded mostly by guys carving very hungrily for it.
The normal way to handle them was boycotting them, and did not interact them on any way on which they could profit.
The automatically given powers, based on contribution, was a very attractive feature. It went very strictly against their own usual mentality.
They were also much more open at the time. For example, it looked that anyone can start a community by them, roughly like on the wikipedia. I even had some project (for example, SE sites on my first or second language, neither of them on English) for which I had used them. Then they have shown their real face, all of these were empty promises. Now I am disliking them as I disliked in the early 2010s.
And yes, their dotnet, closedsource, microsoft, windows line is still causing and always caused a cognitive dissonance by me.
I solved it by doing the lesser evil, but you know, doing the lesser evil does not mean that you are doing the right thing. However, you should actually keep in mind: you are finite being, with finite effect in your finite life. You can not be always 100% orthodox, you should goal to create the largest positive impact.
