Marriage stops people from personal growth and forces a middle-of-the road conformity on both inmates. Some people actually don't grow and thus stay the same as they were when they entered the marriage (I know some), and in that case marriage is OK for them; provided the other partner also shares the non-growth trait. However, as one learns, matures and hopefully gains wisdom, many of their earlier beliefs and "psyche vectors" (for want of a better term) will change. This may mean that their ego construction is substantially different from many years ago. In fact, it might be possible to say that they are a different person; take religious "conversion" for example. Whether their "change" is good or bad (whatever that means) is quite beside the point. The point is that there was natural organic change in the personality over time. This ridiculous artificial idea of needing to stay fixed, I would posit, is the cause of many a neurosis.
Marriage was originally designed to cleave together two nobles houses or bits of land. Quite often the marriagants (ha ha: cute word) would live at opposite ends of the mansion or castle and live largely separate lives. They would "do their duty" and bring forth offspring to inherit the properties and titles and that would be it. Quite often in these houses of nobles, there would be secret doors and rooms adjoining the bed chambers of the marriagants where their mistresses or toyboys would hide while awaiting the time to engage in their lurid relationships well away from prying eyes and gossip. They had a very sensible view of this and had personal freedom for growth (or growth of STDs.. ha ha).
Now in this fast changing and completely unpredictable world, society is demanding that people make long term decisions with absolutely no knowledge of what the future will bring at all. In the past (before WWI) it was possible to predict the future because nothing much changed before the industrial revolution. There is no such "luxury" now. I am irked by the constant self-righteous tongue clicking of those that would condemn people who find the whole arrangement that they had entered into in ignorance now less than satisfactory. And worse: being condemned because they can't adapt to a broken and fundamentally flawed system. If they were to try to contort themselves to fit into such a stupid system, they would only do so at the expense of neurotic outgrowths.
"Think of the children" they all cry. Dr. Phil always says that it is better for a child to be happy in a one parent family (even if in poverty) than unhappy in a family where there is continual conflict and strife. So, please take those "children" off the table and focus on the ridiculous system in the first place. It is better that those "children" learn that such a system is unworkable right at the outset, then stumble into it with some delusional rose-colored-glasses vision.
I am not saying that people should not engage in long term relationships if it is in their interest and inclination. But I am saying that the ridiculous religiosity that underpins the whole marriage system (and its expectations) should be excised like the pustulant infection that it is. In this brave new world, there is no such thing as "long term" any more. A "job for life" is GONE, the only certainty is CHANGE. If a theory (like marriage) runs counter to that, then it needs to be consigned to the rubbish bin of history as a failed experiment.