It seems to me that prenuptual agreements should not invalidate marriages. However, it would appear it's used as one of the excuses for the Vatican II annulment factory to operate.
Anyway, it is a puzzling topic to me.
While I agree it's deplorable to agree something contingent on the possibility of civil divorce, the fact of the matter is that someone signing a civil marriage contract is putting themselves under the power of an anti-Christian legal system that recognizes divorce. Why should the disposition of assets and custody in such a case be under the power of a feminist judge?
It seems to me that the current system is extremely biased. A woman who refuses to sign a prenuptual agreement is more likely to not have the intention to marry than a man who wants a woman to sign one. Someone can foresee the possibility of separation and civil divorce without recognizing divorce or wanting or expecting it to happen. On the contrary, he might see prospective wife's signing of the prenuptual agreement as demonstrating her sincere intentions.
Fortunately, I the possibility of losing property in a marriage is a remote concern to me at the moment. Nevertheless it troubles me when Canon Law seems to enable some of the worst abuses of current civil law, and forbids remedies.
There is no doubt in my mind, that there are more invalid marriages (that cannot be determined as such) contracted by gold-digging women than by men who wish to have some material assurance that their future spouse will not go off to commit adultery with half of their assets.