Interesting idea that extremism isn't a factor among the educated! it's rarely the poorly educated man on the street that starts revolutions, or writes the extremist literature, or ends up in government. Not only that, extremism is subjective depending on who sets the benchmark for normal - formal education generally comes from the same sources that set the ethical and moral guidelines in society so in the mainstream, education can shape the thinking of a population however regardless of the number of times you are told Nazis are evil, drugs are bad and killing people is wrong, there will always be those that disagree or just don't care.
What the Jo Cox case tells me is that in any population, regardless of national ideology, or level of education, there will always be assholes who transgress the accepted, and let's face it, some people will always be attracted by the dark side of the force.
It's naive and simplistic in my opinion to think that education is the answer to all abberation in society, as rebellion is always there in some personalities within that society - education just equips those people with the targets for aggression and the tools to carry out any action they seek to take.