Those people aren't anonymous. The forum mods/admins know who left what tag at all times.

Now, I think honestly, and this is a bit of a stretch... that this might be misconstrued as a limit of the freedom of speech. And that's a slippery slope.

Not that I agree with the tag usage nor the perceived anonymity; however it's not anonymous at all. The mods/admins have allowed it to continue because they can be removed if found offensive and/or reported.