[Svartalfiar]

And referring to organised crime in Italy, he added: "These are baptised Catholics. If I speak of Islamic violence, then I have to speak of Catholic violence.''

The difference being, is that Islamic violence is part of Islam, and is pushed forward by the 'religion'. Catholic violence is generally political or something else, not religious. His Italian mob analogy fails because the violence is due to mob activities, not because they're Catholic. Irish/English violence is due to the English oppression, not because Irish people are generally Catholic. The Crusades were the only one that could possible be considered actual Catholic-pushed violence, except they were responses to, wait for it, Islamic violence!

[Svartalfiar]

So, we could say the big difference is one is Islamic violence, and the other is violence by Catholics.