I was calling BS on the statement that it would be a staggeringly expensive undertaking to provide universal broadband access in the US. It is not, and this is the most important part, expensive on a per subscriber basis which is the only measure that matters. Sure, it would require a total capital outlay which would be large, but that's not the real issue.
The US has roughly twice the population density of Finland. Thus it would be roughly half as expensive per subscriber to wire up the US compared to Finland. The key takeaway here is that Finland has shown that it can be done and has been done.
As to whether it should be a should thing or not, it most definitely should be. The regulatory framework already exists for it, it's called the Universal Service Fund. The only thing lacking is that it is not being used for broadband. That needs to change, but as you said there isn't a legal regime mandating that...
In closing, population density isn't the real issue. Otherwise we would not be lamenting that you can't get broadband in California.
The thing with population density is that it's an average. Averages are notoriously useless for this sort of thing.
For example, the average density of the universe is 3-6 atoms per cubic meter. And that includes things like mountains, people, and stars.
When you're talking about provisioning broadband access, you have to provision for the worst case (or close enough that the differences are insigificant), not the average. Otherwise, you're looking at half the population being under- or unserved.
When you build networks you always work with averages. How many subscribers per mile on average, how many Mbps of IP transit per subscriber on average. Averages are useful and used to determine feasibility, cost and profitability. Population density is a useful average to estimate things with, including network buildout costs.
If you want a better estimator we can use linear density. The US has 321 million people and 4 million miles of roads. Finland has 5.5 million people and 282 thousand miles of roads.
US: 80 people per mile
Finland: 20 people per mile
By this estimate average cost for a network that covers all roads, and thus all permanent residences and businesses, would be significantly cheaper in the US than in Finland.
The US has roughly twice the population density of Finland. Thus it would be roughly half as expensive per subscriber to wire up the US compared to Finland. The key takeaway here is that Finland has shown that it can be done and has been done.
As to whether it should be a should thing or not, it most definitely should be. The regulatory framework already exists for it, it's called the Universal Service Fund. The only thing lacking is that it is not being used for broadband. That needs to change, but as you said there isn't a legal regime mandating that...
In closing, population density isn't the real issue. Otherwise we would not be lamenting that you can't get broadband in California.