There is no such thing as a "public good".
Instead, there is only a tradition that says "the market can't provide this, so we must use the force of the government to provide it by forcing people who don't want it to pay for it".
But that's a lie, and the supposed "public goods" will change from place to place and over time, depending on what the local thieves/politicians want to steal your money for.
Here and now it is roads and "national defense" [sic]. In other places and during other times it has been other things. It wouldn't surprise me to learn that "witchcraft intervention" has been a "public good" somewhere at some time.
If something is wanted (never mind whether it is needed) there will be a market for that thing (or service) and those willing to provide it. No theft or coercion necessary.
Added: a lot more discussion has been carried out here.
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