It wasn't a mistake, but we can appreciate your concern.
Registration was turned on to turn off the incessant posting of the same subject matter. It has nothing to do with yours or anybody else's anonymity. You're still anonymous by making up a username and whatever email address you choose to use in conjunction with it.
Doing so stops certain individuals from acting like 5 different people when they create and reply to their own posts.
It allows the moderation team to remove the same posts that one individual constantly repeats and acts like somebody else under the guise of "guest" posting, ie. They post something that concerns them and then immediately respond to their own post by acting like somebody else to provoke others to comment. If you register with multiple accounts and attempt to make a new post and respond to yourself as multiple registered users, we'll know and we will eliminate all other accounts besides the originally registered account.
It's a waste of bandwidth and our time cleaning it up.