I don't think it is a form of cowardice or something bad. I post on an MMA forum where they have a system like the Cool/sad clicks here, but you can see who gave you a positive rep or a negative rep. And in that situation, people are hesitant to give out negative reps and overuse the positive reps. At least where sad/cool clicks are anonymous, its totally honest feedback.

That being said I'm sure most of the sad clicks are given for stupid reasons. I try to use cool/sad clicks responsibly. I only give sad clicks when I can tell someone is being an asshole, someone is fighter bashing or some other extreme case. I don't use them a whole lot.