> you can inspect, modify and use the code as you can with any OSS, the only things you can't do is commercialize or redistribute it.
That depends on your definition of "use". IMO this is like the the opposite of the GPL and it creates a licensing mess. If I find a piece of code in Sentry that I would like to use in a separate project, that project now has to be licensed under the BSL and subject to those terms unless I can prove I pulled it from some version of the source from however many years ago. And if there's bug fixes to that code, I can't use those bug fixes until the change date expires for those bug fixes. And depending on what license my project currently is, determining if I can even "relicense" as BSL is messy. The end result being that nobody is going to want to use that code in their own projects, and if they do they're likely walking into a licensing mess which they may not even realize.
And that's half the point right? They're happy to take community contributions, but they don't want people using their code. Which, sure, I work for a company that sells software, I'm not against that. But in my view that's not "open source".
Also I think that the assertion that it's "actively harmful" is wildly hyperbolic. Sentry isn't going to be out there copyright trolling people and you know it; they're trying to protect themselves from a very specific category of IP infringement. And there is still much potential upside to it's openness that you're willfully ignoring.