During his visit to Scotland and England, the Pope has warned against 'aggressive forms of secularism,' which he claims exists within the UK. One might imagine that men and women of faith were afraid to walk down the street lest they encounter gangs of aggressive secularists lurking on every street corner.
What do these secularists do? Well, they publish books and articles, appear on television, and campaign and organise to reform the law. Many, such as Richard Dawkins and Polly Toynbee are also atheists and publically express these views. Often they are polemical, but consider also how many religious leaders claim that those without a faith are, by virtue of this fact, stupid or immoral? A common quotation is from Psalms (14) goes "The fool says in his heart, 'There is no God.' " I have seen it posted on church hoardings locally. It continues "They are corrupt, they do abominable deeds, there is none that does good." although they usually leave that bit off.
To be fair, the Pope did not use these words on his visit here and the churches that dislayed it were not of his denomination. But he did make links between atheism and Nazi Germany. Of course atheism and secularism are not the same thing but the atheism movement in the UK, with the exception of a very few hardline communists, is also secularist. Indeed, many people with faith are also secularist; it just means creating a level playing field for people, whatever they choose to believe.
Unlike the Pope, I only know Nazi Germany as history. But any regime that rounds up and murders Jews and Jehovah's Witness can hardly be described as 'secularist.'
Scotland has had and continues to have a problem with religious violence. There is the Protestant/Catholic sectarianism that can occasionally flare into violence. In the UK and beyond there is Islamist terrorism. However, I am not aware of any problems caused by atheists or secularists.