I don’t think that “disagreeing” without explanation is necessarily rude or should be disallowed. However as a personal rule I prefer to provide an explanation.
When I click “like” or “agree”, it would often be superfluous for me to add a reply with explanation. If someone says something I agree with, is it really contributing anything to the conversation if I add a comment which makes the same points? On the other hand, if I have a disagreement that may mean I have a different point of view I can contribute. For that matter, even if my point of view has been mentioned already it may still clarify matters if I explain the specific reason for my response. After all, I could disagree with a post for a hundred different reasons, many of which may be completely contrary to each other.
That’s just my personal preference though and not anything which is expected or required from other members.
