They seem to be second-class citizens, or at least "different." They aren't pushed unless you specify that explicitly. Deletions of remote tags doesn't cause deletion in downstream repos.
I don't agree with lxrec's answer about git having bad defaults.
If you follow the mailing list, you can see that git developpers actually care about having sensible defaults. Would it make sense to have --ff-only as a default? I don't think so.
Tags are not pushed by default precisely to allow a different use than branches: they make it possible to have annotations for your own, local development copy. I would not like to see my why_does_it_break_here and todo_fix_formatting tags being pushed without my consent (those are not actual tag names).
Tagging Tagging a release, on the other hand, is something that occurs less often, and it makes sense to require an explicit push (or use an alias).
I don't see a major difference between tags and branches w.r.t. how push/fetch behaves. In your example, if the garbage tags had been branches, would the deletion propagate as you intended?
When and why would I use a tag instead of a branch?
Generally speaking:
- branches are for trees: they point to different commits over time
- tags are for individual commits and are immutable (this includes frozen trees such as releases)