> The end here (presumably) is a healthy ecosystem

More specifically, the end here is a package manager that doesn't randomly start break your builds because a dependency you need can just vanish from the main servers or lose files you expected to be there. That may or may not contribute to a healthy ecosystem, but it definitely contributes to widespread usage of npm.

if you've been duped into importing a package which has been broadly deemed as spam (but you're not looped into the public conversation about that fact enough to realize it), wouldn't "breaking the build" be a good way to get you to realize your folly and avoid the trap?

No, that is but one condition of the end, but not the whole of the end.

A system is all the parts it requires to continue to exist. Widespread usage of NPM will collapse if everything on it is hot dangerous garbage that infects your CI-CD/dev box with something when you type a wrong character. There are multiple dimensions to trust. Is the package I'm using going to disappear is one. Is the package I'm using a virus is another. Is the entire NPM ecosystem going to collapse under the weight of controlled growth and hosting costs leaving me with nothing is yet another.

You need to back up and look at the whole elephant.