Working on a friend's machine and they had about 200+ tags that were generated by some script or program. They were meaningless and made the tag situation unusable. The following worked to remove most of the tags. It errored out once and when I checked the tags in Finder, they were just the basic ones like Red, Orange, etc.
EDIT: tags doesn't seem to be in brew anymore as of 2016-07-08. Grab it here.
brew install tags
find . | xargs tag -d -N -g -set ''
- Let it run.