So, you’re afraid of anonymous comments. How sad.
I’m certainly not a fan of the preponderance of trolls and morons who feel the urge to treat a discussion board as their own toilet, but it’s also quite possible to go too far in the other direction as well.
You’re in danger of making this into an echo chamber. Sure, simply being required to sign on isn’t going to suppress debate, in and of itself, but you’re choosing to throw out some insightful and intelligent discourse, merely because they choose to not sign in.
Yes, there are morons in that direction, but there can also be meaningful dialogue. However, with this attitude, you’re basically saying that just because someone prefers to remain anonymous, it means (falsely) that they must have nothing of value to offer to the community.
Maybe the real problem is that you don’t like it when your preconceptions are challenged (you’re going to claim that having a login only reduces trolls, but the trolls will be there, regardless, you just don’t like having J. Random Stranger tell you that you’re full of it.) From the last few postings where you had comments, I’m going to have to assume that you’ve taken offense at the idea that most of your commenters hate Markdown (and apparently, that pisses you off).
Login or not, you’re going to have to deal with disagreement, and even trolls. If you think this will allow you to moderate them, you’re just in denial (and even if you are able to moderate them, you could do just as well, whether logins were required, or not).
As to the idea that comments (especially anonymous ones) take away from the thrust of the original post, the only thing I can think to say about that is bullcrap. If your post stands on its own, and makes a clear and identifiable point, it won’t matter if there’s one or one thousand comments about it.
If you really want to manage comments, do it like Slashdot does. Allow all comments, have levels of visibility managed by a group of moderators (here you get around the issue of what one person can do). In lieu of that kind of moderation, the only thing that comes through clearly is that you’re utterly unwilling to accept the idea that people don’t agree with you.