If you're going to call an argument fallacious, then you need to illustrate why. You didn't do that.
If the only option is "Helpful," then the only possible outcomes are that post is shown as being helpful or that post has no rating.
If you have a "Helpful" and a "Not Helpful" option, then there are three possible outcomes: the post is shown as being helpful, the post has no rating, or the post receives a negative score.
In the last case--the post receiving a negative score--you have the potential for that poster to be seen poorly by other members reading the thread. That creates ill-will on the part of the poster towards the members who rated him or her poorly. That creates animosity and the potential for inter-personal conflict.
If the worst that can happen is that your post gets
no score, then it's kind of hard for you to get offended and pitch a snit fit about the rating.
It's for this exact reason why Facebook does not have a "dislike" button, and it works quite well there. I have never ONCE seen anyone complain that someone else's posts got more likes than his/her own.