Nonsense.
Progressives understand the threat of Islam and the radicals. The difference is the left don't demonize all of Islam as the right does. As in not all Muslims are bad or radical.
As for the the christian types Bruce mentioned wasn't there quite a bit of information on the back end of last year stating according to stats that these guys caused more crime than Muslims but law enforcement refuse to call any of it terrorism. I'd have to go look for the articles again.
You have pretty much pulled the conservative card with the statement saying its deflection and demonizing gun owners.
When the guy is Muslim its terrorism. When its a religious nut white guy its mental health with conservatives even if he or she is associated with a group who spread hate and incite violence from time to time.
The right leaning folk in the US cannot see past Muslims when it comes to terrorism. Everything else has to be classified something else. Turn on fox news the day of an incident and immediately they look to Islam as the cause and terrorism before the facts come out. When it turns out to be a white guy its thoughts and prayers and protect our guns and lets move on. No in depth studies or discussions about why there is an increase in young white kids triggered with hate who look to attach themselves to some hate group.
Progressives endlessly attack Christians for bigotry but often won't utter a word to criticize LGBT rights in Muslim countries. Linda Sarsour is a hero of the fringe left, despite her relationships with terrorists and terrorist sympathizers. The media literally hid a photo of Obama and Farrakhan for the better part of a decade. Liberals know that radical Islam is a threat, of course. They're just so obsessed with avoiding any appearance of bigotry (except when it comes to Christians) that they'll contort themselves to avoid connecting terrorism done explicitly in the name of Islam with Islam.
Islamic terrorism represents the huge majority of terrorist incidents in the world. In the US, this is also true so long as you don't carve out 9/11 (which many reports inexplicably do). Terrorism and radical violence isn't limited to Islam, of course. Islamic terrorism also consumes far more of our intelligence, police and military resources than does any other form of ideological violence, and for good reason. That's equally true for the UK.
The world would be a much better place if we could dispense with the ignorant handwringing on these topics. I can "see past Muslims when it comes to terrorism," I just generally don't need to. Pretending there is any other form of radical violence on par with Islamic terrorism in 2018 is simply sticking one's head in the sand.