Slashdot should never have allowed them to begin with, and failing that, should have eliminated anonymous posting many years ago. It was never a good idea
AC posting is a natural consequence of the moderation system and the ability to easily create an account though. If there were not ACs, people would effectively post AC by just creating new sock puppet accounts all the time. If people have lots of sock puppet accounts anyway, it's a gateway towards abuses of the moderation system, etc. Plus new accounts get the benefit of the doubt in terms of posting level, ACs, both back in the past when they did not need an account and now, when they do, are already automatically downgraded. Basically you can't really run any sort of online forum without making some sort of compromises about how people can communicate. My daughter was watching me post the other day and was wondering why there was no edit feature for posts. I explained that it can be like rewriting history, especially if people have already replied, but also if they have read it and are contemplating a reply, etc. While it would be nice if there could be a mechanism to update a post (without removing the original, but to add corrections or updates) without having to create a sub-post, obviously Slashdot made a specific compromise for that. Basically, for the features available for posting, Slashdot picked a certain set of options and, while imperfect, it is hard to say that another choice would have been objectively better.