I really struglle to understand how so many seem to be so on board with this

Headlines like this are why. Just a giant echo chamber of "We're under attack! We're under attack!" getting louder and louder until its the only thing people hear. How do you not get on board with resisting the eternal siege of Evil Empires who are behind every conceivable bad thing happening inside your country's borders? Fighting Russia and China and Iran and <Evil Country To Be Named Later> becomes a panacea. It will cure every ill, because they are the but-for cause of every harm. Only by defeating these evils can Europe reach a Utopian state of existence.