Evidence? I mean, it seems very intuitive: violence has cost, time, materials, and lives. The benefit is you get the spoils of the victims. If the cost for defense is less than it takes to attack, by attrition, you win. The added benefit of bitcoin being unconfiscatable outside of voluntary dissemination of the keys make the attack even MORE costly because now whatever the defender doesn't hold in material wealth is no longer a spoil of war. So, actually bitcoin DOES fix this. As well as it generally more costly to build bombs versus defenses against those bombs.
The reason you think the opposite is true is people are using fiat monetary expansion to essentially get a discount on bombs while there is no such discount on defense. While fiat reigns, and idiots take it as payment attacks are easier than they would be. Just like how war USED to be costly until the income tax made it involuntary to fund war. They used to have to sell war bonds and gain massive popular support.