I'm not sure how.....how is knowing I like history, science and funny pictures bad? Knowing that I think trump doesn't care about this country isn't really bad either as there are quite a few who think the same thing.
Well, If you agreed to ( or realised it most likely would happen) sharing your personal beliefs to unknown clandestine actors. No harm done.
Problem is most didnt agreed to that, or being targeted in elaborate online propaganda schemes.
Its a social network platform, not a blogger system where everything you enter gets published.
Worst thing is that if your friend got mined, so would you