Disclaimer: I started working at FB recently. Consider the following model scenario. You are a PM at a discussion board startup in Elbonia. There are too many discussions at every single time, so you personalize the list for each user, showing only discussions she is more likely to interact with (it's a crude indication of user interest, but it's tough to measure it accurately). One day, your brilliant data scientist…
Predicting political preferences is a huge can of worms. Don't do it. Have the data scientist delete their model.
The observed behavior is the same: using the new model, most people are still shown highly polarized posts, as indicated by subjective assessment of user research professionals.
What should you do now?