If tax payers fund its construction, it's a bit ludicrous to suggest that they should be unable to reap any benefit from it, especially when the purpose of much research is for the public good.

So, only the citizens who fund the research should have access? That, just like the current high-prices, excludes poor countries/people from access.

It doesn't necessarily imply that.

Suppose something is funded by US taxes. It could be harder to restrict access to only citizens than to make it available to the world. For example, should a US citizen who is overseas (eg, on a 6 month sabbatical) be able to access the system?

Or it could be that only downloads from the geographic US are allowed, but further distribution is not prohibited.

Consider an existing journal article written by a US government employees. That work is in the public domain. It is not possible to infringe on the copyright ("pirate") the paper because there is no copyright protection, and in the US there is no "sweat-of-the-brow" protection for non-creative additions like OCR'ed text added to the PDF.

I think it would be an excellent test case to take all of the papers from sci-hub, extract those where the author is a government employee, and have a "public domain sci-hub" version containing only public domain articles.

The lawyer bill would be rather high, so I'm not going to do it. You would likely also have to show that you were actively filtering out papers which weren't in the public domain, and of course reply to DMCA. I can't figure out a business model which would support that. Still, I think YouTube and similar sites show that such a site is not fundamentally illegal.