On balance I can see more disadvantages than advantages to doing it this way. I try to avoid any threads started by GUESTS without labels, because from experience they almost always spin away into futile squabbles. ("Almost always" doesn't mean "absolutely always".)
The posts that open threads tend to set the tone though, and I think posts later on that try to derail things are much less damaging than initial posts which set out to skew a discussion about some important topic in a trolling way. In spite of which I don't favour stopping GUESTs starting posts.
But I would like to see it become necessary to put something in the "From Box" on a post. All right, it'd be possible to put a different name or number in each time they post, but at least it would make it easier for other people to post a comment or reply to it. It is possible to copy the date and time of the post, but doingthat is a nuisance, and it's also a nuisance for any reader who would like to find the post that is being referred to.