I don't think new tags should default to public unless something else about the manage tags page changes -- because how could an admin make a tag members-only or private, then? Would the tag be public until it was first used, and then members-only? Because that seems potentially problematic for members-only comms!

I do often want to be able to make community tags that are public before they're used, but I think that it should require an option pushed somewhere -- make all tags for this community public, or something.