All comments are moderated. So you can expect up till 24 hours till the comment is published. There is a spam blocker in the comments tool. It flags some of the most egregious comments. But there are other reasons to block comments: profanity, disrespectful tone, a copyright violation or some other breach that should not be accommodated, and possibly other reasons.
Comments will not be blocked because they disagree with what I have to say or what students in the class have to say. Someone, however, needs to determine whether there is a legitimate reason to block the comment. That someone is me. I will try my best at this. But I'm human and might very well make an error in judgment. If you believe that is the case, please contact me and we'll try to resolve the manner in a civilized way.