>Who are you to judge how people live and should their lifes?
S/he is just like all the other people who engage in electing law makers that create laws that control how we live. Part of being in a democracy like government is that everyone gets a little say in how we all live our lives with a majority rule. Things like constitutions might mean a super majority is needed for some things instead of a simple majority, but the right to have a say is still there.
I'm not judging. People may live however they want. Institution of marriage is one of the choices, that is established in the society and carries with it some particular set of features. In particular, joining in marriage is somewhat public, even if it's much less public than it used to be. Also marriage comes with explicit (even if not legally binding) expectation you don't cheat. If you don't like those aspects, don't marry; no one is telling you have to, open relationships are fine too.
I'm not forcing my POV on anyone, I'm just stating what is the generally accepted POV in the western society. You may share it or not, but you ignore it at your own peril.
> Who are you to judge how people live and should their lifes?
Churches have no ability to enforce promises with violence or confiscation. And they shouldn't. So it's important for governments to establish some sort of lowest common denominator and hold people legally accountable.
I understand the impulse to be non-judgmental, but when both laws and the rest of society get out of the business of enforcing marriage contracts, you actually take choices away from people that want a stronger marriage contract. They can no longer enter an enforceable contract that requires monogamy.
We're not adding more choice for everyone that way. We're just choosing (as a society) a different lifestyle.
The difficulty in enforcing prenups is partly the problem here, yes.
Let's say you like the marriage rules pre-1970 (no no-fault divorce). You can't write up a prenup that resembles that and have it be enforced by the government (reject applications for divorce and applications to marry someone else).
More options and freedom weren't added when each state adopted no-fault divorce. One option was taken away (pre-1970 marriage contracts) and another was picked (no-fault divorce).
Someone might not like with pre-1970 marriage contracts, but who are they to judge someone else's culture and preferences?
A family's structure and agreements is not public, nor should they be. Unless said family choose to disclose that fact by their own volition.