Thank you for your feedback on the "other suggested papers" section. Your feedback was brought to the product manager to get his response.
His position is that the "other suggested papers" found only on free papers is similar to an ad section. Because the revenue gained by regular ads found on free papers does not cover our costs of providing a free service, the "other suggested papers" is designed to bring traffic and more visibiity to our paying Pro users.
That said, we agree it is absolutely not okay to show erotic content. We are looking into this and will be deploying a fix in the next week to ensure this does not occur again.