The marriage covenant isnt really an issue when you have smooth sailing.
A couple can decide on their respective roles in the relationship; responsibilities, fidelity, parenting, where to live, career decisions... irrespective of if they are married or cohabiting. Like... a married couple can willingly and mutually agree on swinging or an open marriage and still be both faithful and married. Just like a couple cohabiting can decide on monogamy and be faithful to that despite no marriage.
I also think entering a potentially long-term relationship (and you should never marry if that’s not your goal) while focusing on the easiest way out isn’t conductive to success.
I also think that two individuals that decide to cohabit but try to live as separate lives as possible are not likely to reach their goals. Like... if you go on holiday and your partner has to stay at a motel instead of your hotel because of separate budgets and separate incomes. Your house can be just as foreclosed even if you always paid half of the mortgage, and your partner didn’t...
But the real issues arise when the sailing isn’t so smooth.
Like when you die after a long, happy marriage and your sibling, or your child from your first marriage, or your mom who always hated your partner... whatever... might have legal ability to inherit because the home is in your name, or force a sale because half the home is in your name. Leaving your grieving partner homeless. Something that in many states and countries protects a legal spouse from happening.
Or when you are refused admission to the ICU to visit your partner after a serious accident because legally you aren’t related. Something a legal spouse would be.
Or when a collector makes you aware that he CAN take things from your house for the debt your partner incurred without your acceptance or knowledge. Something that many states and countries require that both legal partners sign off on.
Of course, you and your partner can deal with all these issues with legal, notarized memorandums, wills and contracts. On your way to the hospital after hearing of your partners injuries you can drop off at home and get a copy of the medical emergency access permit. Have the hospital legal-team go over it before discussing the next steps in treatment.
Or... you just get married.
"If, therefore, any be unhappy, let him remember that he is unhappy by reason of himself alone." Epictetus