Some of those fall under the "absolutely necessary" exceptions I was referring to.  Things like national defense, roads, some infrastructure projects, etc. just aren't practicable for the normal free market model of individuals purchasing from private business.  A few privately-owned toll roads here and there can work, but it wouldn't work for the bulk of roads to work that way.  That's simply a function that has to be shared, and provided by government.  Same way with national defense, the court system, the monetary supply, and some other things.

That's the threshold I think should be applied to pretty much all government functions (especially at the federal level).

However, government DOING a function is different than government PAYING for citizens to buy things.  That should have limits too, of course, but the bar is somewhat lower.  That's things like welfare, food stamps, Medicaid, Medicare, etc.