And if Facebook knows what issues you care about and what parties/politicians you support, they can easily put all that together in order to sell political advertising campaigns targeting you to specific politicians and give them the specific issues to put in the campaign.
Yes, that's obvious. Would you not expect they to leverage that data point? I don't think there is anything "ulterior" about it...
I don't really see anything nefarious, other than the well known MO of Facebook. People use Facebook and know or should know that Facebook collects data on what goes on at Facebook... I mean "who knew!"
Taking the standard "I can't believe [insert huge faceless corporation here] is spying on my yadda yadda yadda" out of the equation, like you suggest, I think anything to get people more involved in governance is not a bad thing.