What can be done to prevent a spike in racism and nationalism?

I disagree with your characterisation; but the answer is nothing.

People feel as if nothing is being done about this issue, even with this current even the only thing people like Hollande will say is that they'll bring the perpetrators to justice. Perfect, bring members of a death cult to justice (by either giving them martyrdom or locking them up) and all will be well right? Wrong.

The problem has been getting progressively worse, the old theory that time would solve all ills, that as the Muslims who would be vulnerable to extremism gained a better education, a better qualify of life, safety and prosperity, we all end up happy is just over. 2nd and 3rd generation immigrants are more extreme and less open to integration than their fathers and grandfathers, and we have a chunk of an entire generation who grow up having no emotional connection or loyalty to the country of their birth and upbringing, instead feeling more kinship towards a self-declared Islamic State in a region of the world they've never been to.

I think the most immediate reaction will be more self-censorship of the media, which I think has been ongoing with regards to Islam/Islamism for quite some years, I was really disappointed with the reaction today, first with the Telegraph censoring then removing the magazine cover in question, then with the BBC only showing a couple of the more timid covers.

I really wanted to see a united front from journalists, I wanted to see the cover on every Western news station and paper in every Western country, instead it seems the opposite effect is going to win.

Personally I think a phobia against Islamism is not a phobia at all, it's entirely reasonable and rational. If Golden Dawn or a Neo-Nazi group were doing stuff like this we wouldn't hesitate to call it what it is, but when it comes to political Islam we're all too scared to call it what it is; Fascism.

Very sad day.