With all the hubbub about preventing couples from test-driving each other, it is a matter of blind luck to get happiness. In fact, people are to go by traits like pioneer, hounder, Beth Hellite, etc. to judge a potential partner. That is a guarantee that something is not going to work.
This is what can happen when a trial is not allowed:
One "brother" gets married. For the first few months, it is all OK. This "brother" is very controling, and not easily satisfied. He brings his wife to work, often late, from field circus (he is the reason she was hounded into becoming a regular pioneer). Strife builds up gradually, because he is always trying to cram in too much field circus and other things are allowed to slide. They are always in a big hurry.
Some time later, they have a couple of children, thinking that will solve the problems. Instead, it is made worse. The children are now pawns in the conflicts, and there is even worse time pressure because of this. Money issues enter the picture now. Obviously, the marriage is not going to last much longer because this highly controling husband is belittling his wife for taking too long in getting the children ready for boasting sessions and out in field circus. This persists, and of course the wife eventually becomes cold and unloving toward this tyrant husband. Sex is withheld because obviously she does not feel like doing it with someone that is always rushing them past the breaking point. It is only a matter of time before one or both commit adultery.
Had they had a trial run, she would have found out that he is a very controling person. Which is not going to work, if he wants them to pioneer and puts too much pressure on the partner to always get things done. She would have turned him down for being too controling, for the welfare of any children. Or, he would have realized that either he is going to have to be less controling and settle for reasonable field circus time, or be rejected. Either way, it would have been settled (either with amendments before getting together or a breakup before children came along). Little damage would have been done.
But no, the Washtowel Slaveholdery insists that fornication and trial living, even in cases where the couple is serious, is wrong. They put up so many obstacles from getting to know each other intimately before making the final commitment that they go in blind, and one turns out to be a tyrant while the other resents serving him. Better to do the trial and bust it up early than to go in blind, have a few children, and then bust it up.