I think this is common courtesy, but you can't (and shouldn't) legislate morality.

Even if we could not legislate morality we can allow this as a voluntary field. In the case of eBay quite a few people actually use the comment space to defend themselves against negative feedback. Granted, this is not exactly comparing apples to apples, but this could be helpful.

It's courteous to explain why casting a negative vote, but sometimes an Idea is so bloody stupid that it's better just to ignore it.

And sometimes it's in between and you just vote against it without further comment.

On occasion, someone else has already stated your opinions well enough already.

The point of my idea was that this is a forum of people with ideas and the more ideas, the better. If an ideas is indicated as unworthy, it is not a matter of courtesy that the reason for its rejection should be posted, it is a matter for analysis so that the idea might be modified to meet objections. It would stimulate the resource for creativity which is, I assume the basis for this site.

1 problem: What kind of comments will people leave?

"NO" "YOUR IDEA STINKS" "WON'T WORK" etc...

They should give you an option to Say whether your vote is for or against.ANd the Idea poster can choose whether its for or against (If you get someone that is against and they spam the "For" catagory)

But yeah, that should be implemented

I agree there should be some correspondence to a vote. On the other hand, sometimes people just have nothing to input. They may not agree with the subject as well as not have much of an opinion towards it. It is freedom of choice in it's simplest terms. They choose to disagree and choose not to tell you why. :)