This is a tough argument. It really depends on the situation. Let's assume the post above was the dumbest thing one could have said (not saying it is). Knowing myself pretty well, I would have answered it with something like this:
"wow..."
Now after that I could maybe go back to the topic of the thread or change it, which I know it's against the rules but it happens. So, maybe returning to topic or adding meaningful insight to a post wouldn't be a bad idea.
Additionally, you sometimes have that one word answer that adds some humor. And as long as it adds to the thread, and it's not a wasted "lol", I think 1 word replies are fine.