Of course. Blocking same URL would be pretty easy. But maybe the dupe warning in red also warning that it will cost more is better. Incentives seem to work best in Bitcoin and everywhere else.

I think it's important because when one posts a link, the value is not only in the link, but also the community's comments on the link. If the comments are spread out, the value gained from the insightful SN community might be diminished for a user, if he can't find all the other dupes.