Firstly, UK political advertising is highly regulated. There are spending limits, spending reporting requirements, and a general ban on TV advertising outside of the regulated slots: http://www.bbc.co.uk/news/uk-politics-22238582 Most people are comfortable with this especially if the alternative is lie-filled attack ads as in the American system.

Secondly, the context of this is the "fake news" enquiry. It seems that the Facebook advertising and targeting has been used to identify people who are already susceptible to lies (conspiracy theorists, woo believers, anti-vaxers etc) or racism and then feed links to "fake news" stories that were guaranteed to make them angry while encouraging them to share.

It doesn't matter if an algorithm deems that my neighbour finds "relevant" an article on "here's why we should deport all the Poles", it's not an acceptable thing for Facebook to be showing people and they need to take responsibility for it.