It can definitely be more harmful than helpful for some. If you want get bummed out, search out forums for those that were broken up with ("lost my ex"). There are many support forums for such things with people that have been active for _years_ after their breakup. At a certain point they are just ruminating on their pain.

Romantic rejection is one of the most personal and emotional things most people will experience, and having a support network is important for moving on. But something goes haywire for some people given an infinite source of "support" online - unlike with real social connections, online strangers won't tire of you discussing your breakup, so you can do it probably forever, constantly freshening the pain, and peering into everyone elses story for insight on your own...and never move on.