Applying my question on the main site to this site itself:
Can this site, which is trying to be a community for Free Software (besides other topics), run on a proprietary platform (SE)?
Which part of the Free Software community can and will find this acceptable?
Consider for a moment what "Stack Exchange" is really about. Our mission is to share and cultivate open knowledge…and to keep that knowledge free and available for reuse. We believe in that mission deeply and we cultivate it unwaveringly.
But Stack Exchange is not actually a software company. The idea that we have to write software at all is just an artifact of how we get things done. If it were a simple matter of throwing a switch, we probably would have made the core engine open source a long time ago; we talked about it on many occasions. But maintaining and documenting and supporting software in a distributable format is a big responsibility; not something we would have done half-assed or taken lightly. So a decision had to be made about whether to make it about the software… or about what we're trying to do with that software. We chose the latter.
Stack Exchange is actually a huge supporter of open source software and everything it stands for. That's not just talk. You can read about all the projects we do in open source. A few quick examples:
We've provided free vote-based advertising for anyone with open source projects, and have donated $100s of thousands of dollars to organizations like Git, Software Freedom Conservancy, Internet Archive, MathJax, HAProxy, the jQuery Foundation, and OpenBSD.
I'm probably forgetting a bunch, but you get the gist of it..
Literal answer: yes. It's already doing so.
If your question is more moral/ethical, I'm afraid there's not a whole lot we can (or will) do about it. We've convened a community here, and we've got a very good platform to do Q&A on. The fact that it's a proprietary platform does indeed seem contrary to the site's topic, but there's your answer:
The site's topic is the only thing contravened by using a proprietary platform. The site's community don't seem to mind, and the site's only principles are high quality Q&A.
As for the free/open-source communities, if this is the best Q&A site for the topic there is, people are going to come here whether it's closed-source or not.
If you have ethical issues with the site as proprietary software, you must weigh the costs and benefits of your use.
If you think the benefits of using this site (personal enjoyment; public increase of free software awareness on a large platform; support of well-defined community rules and norms) outweigh the costs (using proprietary software and encouraging others to do so via a network effect), then you should continue using the site. If you don't think the benefits of use outweigh the costs of use, you shouldn't use the site.
By definition, everyone here thinks the benefits outweigh the costs. Of course, the cost-benefit tradeoff of a hypothetical site exactly like this one, but run on free software, would be more favorable to you (and others), but no such site exists. You are free to undertake this monumental task of software engineering and community-building, if you wish. (Certainly, hugely-scoped tasks in the past have not stopped free software development, e.g., in building a free operating system. :)
You are welcome also to petition the owners of Stack Exchange to freely release their software, but the odds of this having a positive outcome seem vanishingly small.
There is always the distinction between what is realistic and what is desirable. Sure, it would be better for almost anyone (except Stack Exchange, Inc) if all SE-sites would be running on free software. But realism hits us at two points:
For the second point everyone has to decide if the worse alternatives work for them. As kdopen points out, there are some who think the superiority of the SE-platform beats open source-ness. But everyone has to decide for themselves. You wrote for yourself, that even GNU at some point was created with proprietary software.
For the first point: you can lobby for that on meta SE. Still it's the decision of Stack Exchange, and seemingly they think they make more money if the software is proprietary.
The answers seem self-evident
Specifically to this part:
Can this site, ..., run on a proprietary platform (SE)?
It seems to be doing OK so far, as are all the other sites in the SE network.
SE is not a charity, it is a for-profit organization. If they wanted to run this site off a windows-based server that is their prerogative. So of course it can (as in 'is able' or 'is allowed') run on a proprietary platform.
and then to this part:
Which part of the Free Software community can and will find this acceptable?
Those who continue to come here to ask questions and find answers
By coming to this site repeatedly, they are "voting with their feet" and showing acceptance of the site. The ones who don't like it, will (hopefully) stay away.
