Over the past few years, many prominent news media have shut down comments on their websites. If you spend any time at all reading online comments - anywhere but a few carefully-moderate forums with strong cultural norms around civil discourse, such as Metafilter - you already know why. They are at best juvenile. At their worst, they may challenge your faith in our species.
NPR did an analysis and found that the comments sections, often divisive and uncivil, were serving a vanishingly small subset of their overall audience. The gender of commenters was wildly skewed male, in contrast with their actual listenership, which is nearly 50-50.
Popular Mechanics took a slightly different approach when they noted research that found that ad hominem attacks in online comments could actually alter readers' perceptions of the substance of an article. Allowing comments was doing a disservice to their readers' ability to understand the science they were reporting. The Nieman Journalism Lab reported on what happened after Popular Science and several other media outlets disabled comments.
Incidentally, I switched off comments on this site. Not because it had become a hotbed of scum and villainy, but because it wasn't really a hotbed of anything. Use of comments was pretty infrequent, and there are other clearly-marked means for anyone to follow up with me. A little scum and villainy might have been exciting... for a few minutes.