The main criticism that is valid is the "gunshy enforcement" by FSF, but if you listen to people like Eben Moglen they are very open about the fact that they have been working on the long game of getting into a position where enforcement would be effective instead of weaken the copyleft movement via a failed enforcement action, and that they have known it would take many years and even decades before the law side would catch up and be ready. I do think they need to step it up, but these are things that FSF et al already acknowledge and are working to address.
I have to admit a certain amount of conflicting views here, as I am at the same time sympathetic to entities afraid of doing work that others might then use and profit off of without contributing back (such as MangoDB claims), but I am also sensitive to claims that the licenses they are pursing could also be used as a cudgel to get more people towards paying them instead of using FOSS versions, and also to the fear of corps that SSPL could be a dangerous license if misconstrued. Which is why Mongo was dropped by RedHat, Fedora and Debian...
In general I think that (a/l)gplv3 did most of the work actually needed to solve these issues, and that attempts like SSPL, however laudable, are likely to fracture and weaken FOSS as a whole and, being incompatible with gpl, I cannot support them. There are ideas there that are important and should be discussed however.
I have put my actions where my mouth is on this issue. I have worked very hard to make the majority of my daily desktop and server stacks gpl or gpl compatible. (which means I steer far clear of mit/bsd licensed things if I can) The few exceptions are things I always keep an eye out for alternatives on.
An interesting SO on the SSPL: https://opensource.stackexchange.com/questions/7522/sspl-and...
In essence, I mark it as a sign of honest discussion when someone admits the weaknesses to their arguments. There is none of that here, ergo...