Leaders of Islamic communities in England last week wrote an open letter pointing out that government policy and programs are infuriating young men and are in part, the cause of terrorism. British leaders responded that that was blackmail, and that governments couldn't possibly make decisions in order to prevent terrorist attacks.
So...let's just unpack that interesting statement.
First of all, blackmail happens when someone secretly threatens an illegal or immoral action unless the receiver accedes to a demand. (pay money being the classic demand). Blackmail by definition doesn't happen in public. It by definition is an illicit activity, a kind of bloodless terrorism. And it only happens between two parties. If I say to you that if you don't stop doing X, someone else will take revenge, that's not blackmail, that's a warning. Warnings may be unwelcome communication, but they are not blackmail.
So it was plain old racist of British leaders to respond to leaders of the Muslim community's letter by calling it blackmail; that was implying that those leaders were themselves responsible for the illegal and immoral activity of a few young men. Nor do I think that Christian leaders would have been called Blackmailers under similar circumstances; such nasty words are used only for the despised.
And as to the question of whether a nation should take into account the activity of terrorists in forming and executing its foreign policy... in the "new normal," they should, do, and will. Not necessarily give in, of course, but count the costs, in advance.