FB has been forcing video explanations on our feed that tells us we shouldn't worry. They're wrong.
Our data can be used against us
Just because only our names won't be sold, it doesn't mean we're protected. Afterall, we're the targets of the ads being served. When you can selectively show anything to anyone, this is turned into a weapon.
Mass manipulation
If you tell people things they are inclined to agree with, they probably will. Like shown in The Guardian, this was a major factor to get Trump elected. Different campaigns directed at certain groups were used to push people into siding with the current USA president for one reason or another.
Xenophobic ads and posts aligned with his political view would show up in the xenophobic voters' feeds, but not to other Trump-inclined individuals like those whose profile show potential for the Family Planning promise (which has been defunded) and vice-versa.
Spreading hate
If you want to find a lot of people to join your nazi group, Facebook will help you do that. It's easy to filter through the options to quickly set up a hate group. You could even restrict your promotion to local areas and finally get your own neo-ku-klux-klan going. All thanks to Facebook.
Don't turn a blind eye
The safest countries in the world's population have the habit of keeping an eye on their friends and neighbors, asking questions in case someone is acting strangely and reporting them in case they think something dangerous is up. You can do something similar on FB.
Noone will know when you snoop into your friends' profiles to look at what groups and pages they're into. This habit should be practiced by everyone. It also helps to point out potentially dangerous personal and/or professional relationships.
Be careful out there.
Thank you for reading!