Until divorce was codified marriages were often brutal. Even today, we read stories about countries in which divorces are so difficult that women are murdered (sometimes by their mothers-in-law) because it is easier, and cheaper, than divorce.
Without the possibility of divorce there is little, if any, accountability within a marriage. And while you might think that such freedom therefore runs both ways; that is seldom the case. There will always be people who do their best and give their best, no matter the circumstances. There will always be bullies. There will always be people who are just stupid or lazy, or both.
In my practice we very rarely see two people who have both simply outgrown each other and want to move on as friends. Although we almost always get to that point, divorce usually begins quite differently.
Most divorces begin with one partner who is completely blind-sided, confused, sometimes heart-broken (sometimes referred to as Defendant), and one who has suffered for years and cannot take it any longer (or, typically, Plaintiff). Plaintiffs usually think they have tried every possible way of asking Defendants to change. Defendants have no idea what the Plaintiffs are talking about.
Without safe, legal, affordable, accessible divorce, those Plaintiffs might well spend the rest of their lives suffering at the hands of a Defendant who cannot hear them. Escaping the bounds of a marriage in which they parties cannot understand each other can be a very helpful and necessary change – for the Plaintiff, but also for the Defendant, and any children they share. (Also helped by this emancipation are frequently all of the friend and family of the Plaintiff, who have suffered along for all of these years; and sometimes even the family & friends of Defendant.)