Yes, it's insane to think about a current member of NATO wanting to invade another member. But that's why major wars usually happen, insanity. Hitler never had the means to carry out his plans, it was his stupidity that caused him to wage war against enemies that he could never actually defeat. There are still insane militaristic groups that could come to power in a country with a massive military. But NATO makes it abundantly clear that such an expansionist war cannot succeed. It's not just a defense force against Russia, it's a defense against a world war between forces that could tear the world apart if they fought. It's of utmost importance to preserve this peace treaty.