Back in the days of network TV, you might not agree with everything that was being said, but you could at least see the arguments that were being used to convince others.
Even the early so-called behaviour change campaigns, such as 'Five a Day' (a marketing campaign that most didn't realize was a marketing campaign that has long since been accepted as a piece of general health advice) were quite benign.
Here it seems that an influence / behaviour change campaign could be waged relatively cheaply against a relatively small number of people, exist completely outside the normal rules for fact checking or veracity, and the majority of the population would have no idea about it.
I'm not sure I agree with the thesis of the piece - that Cambridge Analytica played even a primary role in Brexit happening (I think it was always pretty likely, due to UK tabloids having campaigned for around 20 years on the issue, lack of organization in the Remain campaign, Corbyn failure to engage working class voters etc, hell even a latent feeling that the EU maybe isn't that great after all), but the techniques for doing this will only become more sophisticated and I wouldn't be surprised to see them become a common feature of our democracy.