If you don’t want it to be open, don’t make your code open. (It’s not open by default.) If you do, don’t be surprised or dismayed when someone takes you up on the offer you created.
I don't think we need software Manichaeism. Software can be as open or closed as anyone likes with many degrees in between.
It is preferable for everyone to have software that is relatively permissive but has barriers in place as to not run into a tragedy-of-the-commons like situation where large companies simply take the code of small innovators wholesale and profit off their work without contributing back. License extremism is silly.
Why would we be better off if sentry completely closed down their source code, thus robbing everyone of running and using sentry themselves?
BSL is just better proprietary licence. It definitively isn't open source. I think of it as better way to do shareware.
But there is big difference between shareware and open source and we don't want to muddy it.
If all you do is use sentry internally (which is a major use case for this particular piece of software) you can do what you want. This is not at all close to a proprietary license.
Can I sell this product as SaaS ?
Can I put that code in a library that would be usable by SaaS product ?
Who decides if it competes with sentries ?
How about if sentry suddenly adds functionality it didn't have before, so now it competes and before it didn't.
Or maybe they don't get to do their IPO and are bought out by oracle(or similar). And their lawyers smell an opportunity ?
If this code would be any other standard open source licence the answers is simple. I don't even have to ask anyone.
But sure if I wanted to use it mostly like flexible shareware internally I can do that.
I think that's a fair decision for them to make and license their code accordingly.
They said very explicitly in the article that this is technically not "open source"
I do disagree with the use of “technically” in the last line. It’s simply “not open source” (which is, of course, fine).
There are more things than the extremes.