That is a very naive and unrealistic mentality, bordering on the kind of idealistic views I had when I was in my teens. By making a pre-nup or similar you are not setting up to fail, you are just taking sensible precautions in case the worst happens. Marriage isn't an episode of My Little Pony, it's a löegally binding commitment where if the worst happens your life can be destroyed. There are enough stats and experiences with broken marriages for the last few decades to be able to know that there IS a chance you will get divorced, and only a fool would not take that into account when getting married.
Sadly, the finer points of this kind of psychology are lost on most people... they only see sense when it's too late!