I think it is much better to be sure, before doing something, that you are doing it right.
If you are going to plan for every possibility of failure, then you are going to do it 24/7, never even getting to having considered 0.000001% of all potential failures.
If you've chosen your partner well, if you know that this is what you want with absolute certainty - then the probability of failure is minuscule. And if you are getting into a marriage consciously thinking that it may fail, then, I think, you are doing something wrong...
I mean, sure, if you want to do prenup, go for it, nothing wrong with it. It is when you say that doing it is the only right way to have marriage, that it starts sounding a bit paranoid.