The usual protest is, It anticipates the failure of a marriage before it even starts.
And it's not a bad point to make, and addresses the sentiment behind it. What does this say? Lack of trust? Well, people change, especially over such long periods of time, and the better focus going in is your OWN sense of commitment. Nevertheless, it's an understandable reaction. But I have a totally different reason that I think is extremely important and foundational for a relationship for why a woman (many people's view of the current climate) SHOULD sign a prenup, and it has nothing to do with the actual anticipation of potential failure.
If Western women are good at anything, it's coming to their own defense for their own interests. And in principle, that's a perfectly good thing. The problem is, they also almost always despise men doing the same thing for themselves: protecting their own well-being and interest and protecting their own interests.
A man very well should say to a woman: I shouldn't have the right to have a marriage where (for example) a woman compromises her earning power to focus on traditional domestic duties and/or raising kids ("stay-at-home mom") only to be able to run off without compensating her for what she contributed at her own expense. A woman SHOULD see a man's belief in that -- good for her.
GOOD! And again, what can we pretty much always count on with Western women? They're experts at looking out for their interests like this, on a level of principle. But the question is, can she actually say the same thing to a man, not just: "I would never do that to you," but also: "I should not have the RIGHT to do that to you"?
See the woman can do the same thing: renounce her ridiculous modern abilities to wipe out a man financially for divorcing at a whim (as mentioned, not alimony altogether). THAT is what signing a pre-nup says.
I'm sure some people will dispute the situation but the general principle should be agreeable in concept. And, these are just my observations of the landscape of things.