Italian fascism and German Nazism fell apart because the majority of people didn't actually believe in those ideologies, they were forced into them for fear of reprisal.

Not true. The majority of germans and a significant portion of other europeans were believers and supporters. The majority were willing contributors. Fascism and Nazism were destroyed by a relentless unquestionable military defeat. The most devastating war in the history of mankind.

They also existed almost entirely within those countries (making them easy targets).

While antisemitism was a shared ideology across the western world, be it amongst the gentile elites or the general population, and fascism was very much en vogue and seen as a progressive, modern answer to the "decadence" and corruption of democracy, you are right that there was a defined territory where the war could be waged.

They don't even have a centralized ideology - it's a culmination of various ideologies.

The central ideology are the Qur'an and the hadiths. It's all in there. Also, you underestimate the decades-long efforts and influence of the muslim brotherhood, the basis and roots of the islamic "uprising".

If you bomb ISIS into the dust then you just set off a war against Sunni Muslims, possibly ALL 1.3 billion Muslims, all around the world. There's Muslim's living in every single country. What are you going to do, deport everyone because of their religion?

A world war is what will need to happen, exactly like in the case of Nazism - if we don't act now by stopping muslim immigration and deporting every single muslim in europe.

What is this, 17 century Europe again?

No, this is 21st century middle eastern culture.

What we need is a militant progressive democracy. That acts rational and consistent in the fight against its enemies.

Every single muslim, by submitting to the belief that a mentally ill, child raping, mass murdering warlord is the greatest human to have ever lived and was given the final and ultimate truth about the nature of the universe, is our enemy.

Just like every Nazi is our enemy.