Often there are strong personal attacks when someone makes a comment. Perhaps just being able to click disagree would take away the personal attack and the discussion may remain more civil.
On a different note, many comments within minutes are inundated with likes and I can't help feeling they are not genuine. If someone is using multiple devices as well as multiple names, they can sway the number of likes to provide added ammunition towards their argument. If there was a disagree button, at least those disagreeing could also be logged.
Anyway, this is a suggestion and it might be worth knowing how others think. If I hear a strong argument against it, it might make more sense than my suggestion. On the other hand it just might prevent me getting nasty comments on thoughts which are not as negative as the nasty commenter might try and suppose.