Your arguments in this thread seem to be coming from a single point of disagreement: the point and definition of "Open Source".
> We want to compete on the flexibility aspect of open-source - the fact that you can change the code however you want as per your needs, the fact that you can deploy it however you want (and hence have complete access to your data)
This does not cover the point of Open Source. The point of Open Source is _open collaboration_[1]. Putting a restriction on use discourages open collaboration.
Take your chosen license, for example. If I wanted to improve your code, licensed by you to me under the SSPL, I'd add my own code to it. Sure, the code I added would need to be released by me under the SSPL too, but I would still retain copyright on my code. Now, if you liked what my code did and wanted to use it, _you_ would be subject to the SSPL too. Would _you_ be willing to comply with the SSPL, for my code, especially when the SSPL cannot be legally complied with[2]?
Now, the creators of the SSPL can get away with it because they aren't subject to it themselves, because the retain all the copyrights of all the code they release, and do not accept any code from anyone without also demanding a copyright transfer to them. This is complete ownership, not collaboration.
There's a reason open source distributions, who have no intention of competing with MongoDB Inc.'s business, stopped distributing MongoDB in their repositories. I will just leave Fedora's opinion on the matter as supporting evidence[3].
The copyright argument on code contribution is orthogonal to the license. You are free to fork the repo and make whatever modifications on top and own the copyright on the addition but if you want to contribute code back, pretty much all popular open-source projects would want them to assign copyright back to them.
Licensing will govern what you can and cannot do with the repo you clone or fork. SSPL is GPL except for this additional hosting clause for service providers. So, the argument on whether it violates open_source ethos or not has to be around that clause.
> We want to compete on the flexibility aspect of open-source - the fact that you can change the code however you want as per your needs, the fact that you can deploy it however you want (and hence have complete access to your data)
This does not cover the point of Open Source. The point of Open Source is _open collaboration_[1]. Putting a restriction on use discourages open collaboration.
Take your chosen license, for example. If I wanted to improve your code, licensed by you to me under the SSPL, I'd add my own code to it. Sure, the code I added would need to be released by me under the SSPL too, but I would still retain copyright on my code. Now, if you liked what my code did and wanted to use it, _you_ would be subject to the SSPL too. Would _you_ be willing to comply with the SSPL, for my code, especially when the SSPL cannot be legally complied with[2]?
Now, the creators of the SSPL can get away with it because they aren't subject to it themselves, because the retain all the copyrights of all the code they release, and do not accept any code from anyone without also demanding a copyright transfer to them. This is complete ownership, not collaboration.
There's a reason open source distributions, who have no intention of competing with MongoDB Inc.'s business, stopped distributing MongoDB in their repositories. I will just leave Fedora's opinion on the matter as supporting evidence[3].
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1: https://en.wikipedia.org/wiki/Open-source_model
2: https://news.ycombinator.com/item?id=18301116
3: https://fedoraproject.org/wiki/Licensing/SSPL