Can you elaborate? People are worried (rightfully so) that this feature requires uploading via the Facebook Messenger App. But this means they don't have to visit a URL or download another application.
Now, it's fair to say that even in a technically safer implementation where the photos never leave the device, many users can't tell the difference, so this point doesn't hold a lot of water.
Still, I think making the uploading of scandalous photos to FB is a dangerous precedent to set in general. Will other services and startups that have users suffer from the same problem implement this feature in the same way, and guarantee user safety and privacy? That's a pretty high bar.