Before I get into this, let me just say that I 100% agree with your post. But since this hasn't been resolved yet (and since I'd like to address a couple other tags too), here's my formalized proposal, which can be met with up- or down-votes to reflect a community consensus:
government, civil-authority, church-and-state, government-laws should all be eradicated and united under one new tag:
civil-government. All questions with these tags are about either 1) how Christians should relate to those in power, or 2) what Christianity teaches about what civil government should do.
Why give it a new name?
None of those tags do it justice yet. church-and-state and government-laws are overly specific, government is ambiguous, and civil-authority is not likely to be found by someone looking for a general "government" tag.
Alternatively, I'd be fine with using civil-authority and having
civil-government be a synonym. That's a minor point, and people can weigh in on that in the comments here.
Why are these tags closely related enough to warrant one tag?
Firstly, I'd like to repeat that I 100% agree with you:
I'd still argue that the distinction between civil-authority and government will be lost on most people: not just the ones posting questions, but also the ones using tags to explore the questions on this site. It seems to me that keeping them separate and making an effort to maintain the distinction will produce more confusion than navigation.
People using the tags for navigation will be looking for questions about how Christians relate to the "governing authorities": police, judges, elected officials, etc. Being overly specific will just be confusing. People asking the questions will be very unlikely to keep a distinction in mind either, and we'll have to keep a close eye on tag maintenance. A bit of a bother.
If questions are about the separation of church-and-state, then they're about both uses of the proposed
civil-government tag that I mentioned above. If they're specifically about the United States, then they could use the
civil-government and united-states tag; no need for a dedicated church-and-state tag.
If questions are about government-laws, then they are no doubt about one or the other (or both) of the uses of the tag mentioned above. No need for a dedicated tag. Most questions about the government are about laws anyway, and all questions about laws would also be about the government. This is a classic "tag synonym" candidate.