Well, I think your first mistake is assuming everything is rational and reasonable under the law… It doesn’t always work that way. A lawsuit is essentially a series of calculated risks. I’m sure you’ve known someone who has divorced? In some cases wonderfully normal people can turn from rational to emotional – even vengeful – very quickly. Especially when children are involved. People can lose that rational perspective.
First off, it’s impossible to answer your question for a couple of reasons.
1. The laws of divorce vary greatly between states. There are fault and no fault states (I think there are still fault states) – this makes a difference in how a divorce is granted (i.e. in some states you have to prove that someone was “at fault” i.e. adulterly, abuse, or something and in some states you don’t). Also there are community property (everything earned during the marriage is split 50/50) and non community property (you keep what you earn) states. Some states allow for alimony in the statutes, some do not. Basically, because it is regulated by the states and not the Fed gov’t, a huge part of your question would depend simply on where the couple lived in the US. Then the default rules of that state would apply – some states seem more equal than others – depends on your definition of equal. So a pre-nup may also protect you in case you move to a different state with different divorce laws than where you were married (assuming the new state recognizes your prenup)
2. “Fairness” cannot be determined by one individual. Should everything really be 50/50? what if one person simply contributed more to the marriage? And how would that even be determined? what if the couple never agreed one party would stay home, one party just stayed home because they couldn’t find another job? Should they still get 50/50?
3. So much of this depends on how much time and money the couples want to spend fighting this out. In the linked example above the woman was fighting for her “fair share” but she ended up spending all of their money. Sometimes couples can be rational, sometimes when someone cheats or thinks someone cheated (or any number of other things) a switch can be flipped and one party is out for revenge.
4. There are different types of divorces. Couples can do mediation, collaborative divorces, self represent, or go to court with attys for the trial. It depends how the couple wants to resolve it – actually it depends on how one party wants to resolve it. If one side isn’t into a collaborative divorce or mediation, it’s not going to work well. Generally, if you’re in extended litigation the party with more $$ is going to have an advantage. Like the linked example above where the man could no longer afford and atty and had to represent himself. I imagine it would be difficult for a non-lawyer to litigate a divorce against a lawyer who knew all the laws/rules.
5. You can’t simply trust the law because there are too many unknowns. The law may work in your favor today, but you don’t know if the legislature will change it, you don’t know who your judge will be, you don’t know if the judge will be having a good day when your trial comes up, you don’t know that your sig. other isn’t going to change in the future (yes not a romantic idea, but sometimes addictions, mental illness, or anything else cannot be predicted)… I think the pre-nup tries to take the uncertainty out of it.
6. Sometimes pre-nups are set aside by the courts or the couples. I really wouldn’t know the details as to why, but it happens, and it’s an option.
7. Most importantly I think the point many people miss is that a pre-nup does not just plan for a divorce. A pre-nup can do amazing things to level the playing field during marriage. For example: if one partner has lots of unsecured debt (let’s say in student loans) then when married that debt could prevent the couple from getting a mortgage loan. However, if you assign that debt to the spouse that incurred it, then the partner may be able to get a mortgage loan in their name alone and not have that unsecured debt taken into consideration – therefore helping the couple/marriage by allowing them to get a home they couldn’t have without a prenup. There could be different tax reasons to get a prenup. Maybe if one partner owns a business the prenup can protect the other partner in case that business goes bankrupt, thereby always keeping one member of the pair afloat. Again it’s different in all states, but those are some other ways a pre nup could probably be used that don’t relate to divorce, but rather contribute to the quality of the marriage.
Sorry for the TL;DR. I’m by no means a divorce lawyer, but I think it’s probably very difficult to understand the US laws when you’re outside the country because there are 50 different rules about divorce in this country. Sounds like the laws are purposely made to be fair and equitable and apply to everyone where you are. But here it kind of depends on which state you live in and what you think is fair at the time of your divorce. It’s all a matter of perspective.