I don't see the problem with boost? Isn't that a perfect example of your well supported, community embraced option? I certainly feel much safer pulling something in from boost via the official debian repos than I do pulling a random package with npm or cargo or etc.

Primarily I think the underlying concern has to do with the pathway for authoring code. When you have contributors whose submissions are gated with a rigid third party process and where that third party is the one responsible for curating the code (as opposed to the author also being the curator as well as the publisher) then you have the possibility to catch a lot of wrongdoing before it succeeds.