not a teacher
I would hit "Disagree" but go on to make another post.
I must admit that I can't see any purpose in the "Dislike" option.
I understand your point, emsr2d2, but in fact it's not a "Disagree" but a "Dislike" button. If I disagree with an opinion, it seems to me that the best option is to post a reply. If I post a reply with a differing opinion I don't see the need to say that I "Dislike" the original post.
As the vast majority of people, including learners, respond here in a genuine attempt to help, I imagine it could be quite discouraging to have native speakers "Dislike" your post, when all that's required is a clear explanation of the error and a referral to the guidelines. I think that such situations have been handled well in the past without the need to pointedly "Dislike" somebody's efforts.
If somebody genuinely dislikes a post because they find it offensive or culturally insensitive etc, then there is the "report post" option. I have never reported a post but on the rare occasions that a post has seemed problematic to me, again, I have found that the moderators have handled these situations promptly and well.