Other than thinking that paying for political advertising is rather less worrying than various other ways countries have gone about trying to obtain their foreign policy objectives (wars, exploding cigars, etc), I am not sure what I think about it.
But I am sure that some people who are thinking about it are getting it completely wrong. I was struck by the reference to the Irish abortion referendum. Here is more from Gavin Sheridan:
Hmm. Is the real worry here that your mother and father - what are talking about? 50, 60, 70- somethings? - will be swayed by "anti-choice" ads on Facebook paid for by Russia? I don't think so. Russia had the highest number of abortions per woman of child-bearing age in the world in 2010, according to the UN. Meanwhile, George Soros is known to be funding pro-choice (let's be civil about this - the two sides go by 'pro-choice' and 'pro-life') campaigns in Ireland.
I am pretty sure that Facebook ads during the Irish abortion referendum are going to be (a) aimed at younger demographics than "your parents" (i.e. at the people who are actually influenced by what they see on Facebook), (b) pro-choice and (c) often funded by foreigners (i.e. non-Irish people) pursuing their own agendas.
If you are on Facebook and come across a well-made, heart-string-tugging viral video about (say) a teenage girl in difficult circumstances, you may be on the receiving end of foreign propaganda. How you feel about that fact should not depend on how you feel about the message in the video.