Could you demonstrate the direct link between The Mail etc. writing 'racist drivel' and the rate of terrorist attacks.
Of course not, but one should take an educated guess and imagine a scenario where 90% of the media in a country write at least an article per day on how bad Muslims are is going to annoy someone, then realise that we live in said country.
This translates to readers opinions and their interactions with others, communities start self-segregating as they have (though that's rather natural i'd imagine), and the idea that said "areas" are **** holes devoid of good people makes it all the more likely that it'd be a source of a terrorist.
But you know, lets wait a decade for a study to say it?