The problem is though Martin, you will have an exponential increase in societal violence as men…
Matt Miller
1

You raise some interesting points. I’ll address them in the order you raise them. 
The problem is though Martin, you will have an exponential increase in societal violence as men begin confronting each other over sexual infedelity, and as more men are kept away from their children.
There are two separate things here. First, why should there be an increase in societal violence, we already have considerable infidelity, but it rarely causes violence? Surely the opposite would be true; if there is no marriage there can be no infidelity. 
The major reason for problems with fathers access to children is the resentment engendered by an obligation to maintain a rocky marriage and the confrontational nature of divorce. It is hardly surprising that under these circumstances the divorcing couples build up a desire to hurt one another. 
Another obvious thing that is an outgrowth of open, do-as-you-want approaches to sexual ethics, is the death of marriage.
So what? Why should marriage be encouraged if it isn’t of benefit? 
But, as men keep being thrown under the bus financially, and as parents and husbands, who are now going to be told they just have to lump cheating wives, men will cease offering marriage.
If there isn’t any marriage, or marriage is non exclusive, wives, by definition, won’t be cheating. You can only cheat if you promise to be faithful. 
I think we should reserve marriage exclusively for those who want exclusive, committed, monogamous relationships, and those who don’t want this can do something else.
I would agree, but the problem is that the overwhelming majority of people who get married believe they want an exclusive, committed, monogamous relationship; that is what the madness of romantic love induces. Once the shine of this wears off many find that they have promised something that is either difficult or impossible to maintain.
How men and women will negotiate the changes that the emancipation of women must inevitably bring about in the sexual relationship between the sexes I don’t know, predictions are very difficult to get right. However, I am optimistic, men and women lived together in harmony for hundreds of thousands of years before marriage was invented.