Is a one column table good design?

If there is a valid need for it, then I don't see a problem. Maybe you just want a list of possibilities to display for some reason and you want to be able to dynamically change it, but have no need to link it to another table.

Yes, it's certainly good design to design a table in such a way as to make it most efficient. "Bad RDBMS Design" is usually centered around inefficiency.

However, I have found that most cases of single column design could benefit from an additional column. For example, State Codes can typically have the Full State name spelled out in a second column. Or a blacklist can have notes associated. But, if your design really does not need that information, then it's perfectly ok to have the single column.

I've used them in the past. One client of mine wanted to auto block anyone trying to sign up with a phone number in this big list he had so it was just one big blacklist.

In terms of relational algebra this would be a unary relation, meaning "this thing exists"

Yes, it's fine to have a table defining such a relation: for instance, to define a domain.

The values of such a table should be natural primary keys of course.

A lookup table of prime numbers is what comes to my mind first.