There are a vast number of situations where the individual decisions about how to spend money/take action may be the best for the individual, but bad for the society overall. For each and every one of those, it's better for society to act as a unit to make the optimal decision.
> For each and every one of those, it's better for society to act as a unit to make the optimal decision.
Depends on how you define "better". Who is to say that "better for society" trumps "better for the individual". There's no particular objective reason to take that position over the one favoring individual choice.
> If everybody owns something, then nobody owns it. We should probably rethink our notion of what "the commons" means, vis-a-vis property rights.
Good point. Of course, that rethink might go in either way, moving more things from public to private or from private to public. It's a good idea to periodically review what we consider public property and try to make it more consistent with the idea of privatizing externalities.
https://en.wikipedia.org/wiki/Tragedy_of_the_commons