There are many situations where a news site can get insight from users especially anonymous ones, such as those involving minor children etc. Reporters can then use those comments to follow up with school authorities or companies...

it's a great way to get story ideas, I really don't see the downside..Except that a lot of journalists don't bother to read them & miss the opportunity

The biggest risk is that the "reader comments" are actually from companies promoting/defending themselves. If you can view the backend of your site, though, this is usually pretty obvious since most of them don't bother to go outside the company internet to do this...