I think this is an oversimplification, just as others criticizing multiculturalism. Islam has 2 billion people, so if it was just Islam being this way by default then the whole world would be unabated chaos. However, they are pulling people from areas where there is poverty, war, radicalization, and a history of offenses by the UK against it. You would have to be a total moron to think you won't end up bringing in radicalized people who feel they need to get revenge against your country.
So I think this is actually a failure of multiculturalism because an essential component of that is UNDERSTANDING each culture. It does NOT mean giving blanket acceptance and approval to anything at all from any culture but rather understanding that each one has strengths and weaknesses and histories with grievances from enemies and shared agendas with allies and being realistic about that and holding everyone to the same principles of accountability, respect, justice, and self-responsibility.
If you do not do this, if you hand-wave atrocities as "different culture" then you are not viewing or expecting of them the same dignity that you do other peoples. You are saying that craven acts of violence and criminal plotting is just what they are. That is a racist position that would come to all the same results as the colonial offenses that built such a disdain between parties in the first place, just like ignoring the cries of victims spins up vigilante action and blanket race-based solidarity response.
So I would say these results are actually a huge failure at the principles of liberalism. They are racist and classist, holding different peoples to different standards, and completely giving up on the possibility of understanding each other or living up to shared foundational ideals and principles. This really needs to be pressed with everyone protecting the criminals. By overlooking or downplaying their crimes as cultural difference, you are dehumanizing them, acting as though such a nature needs to be accepted because one ought to expect less of people like them. It is the true racist response, not the response holding them to equal standards of law and justice.