I completely agree. I would only add that there have also been arguments about whether GPLv2 is discriminatory, though they also feel long behind us now.
There is always a case in which all license will be discriminatory when it comes to "specific fields of endeavor". If the endeavor is to break copyright then a copyright license can't permit that. To take a example, permissive licenses do not allow someone to take full ownership of the copyright of someone else work.
As such the Open Source Definition with the phrase "specific field of endeavor" is limited to cover areas which don't involve copyright law. For many reasons, including copyright law itself, it can not grant that which would be the most broad definition of nondiscrimination.
You own sentence shows the relevant difference: "embedded". The GPL license has always stopped at the OS process boundary. You can essentially do whatever you want with a GPL program as long as you interact with it over standard OS mechanisms, rather than direct modification; you're still obligated to distribute source but it's source that is already publicly available, so there's no proprietary interest in it. Mongo's does not. Neither does the AGPL, to show this isn't new.
> The GPL license has always stopped at the OS process boundary. You can essentially do whatever you want with a GPL program as long as you interact with it over standard OS mechanisms, rather than direct modification
Not strictly the case according to the FSF's FAQ; the GPL applies to anything that integrates deeply enough with the covered program to constitute a "derivative work" under copyright law, which is not necessarily the process boundary.
> Neither does the AGPL, to show this isn't new.
Indeed - so what is RedHat's rationale for permitting AGPL but disallowing this MongoDB license?
> The GPL license has always stopped at the OS process boundary
No, it stops at the copyright law boundary of derivative work.
Whether or not a court would find that to be equivalent to an OS process boundary probably varies by jurisdiction and detailed facts of particular cases.
You absolutely can run GPL software embedeeded however you feel. You can't distribute it without meeting the conditions, however (and some database software providers think distribution within a company counts as distribution, so there's that)
You can't run it using closed source management software to offer MongoDB as a service.