My personal opinion is that everybody should do it, for at least a year.
However, that is based on my own concept of what marriage is. And as is always the case with any discussion related to this topic, we return to that same question, of what marriage means to YOU. And that is not going to necessarily be identical to my own notion!
I agree, though, that it can be easy, especially for younger people, to decide to live together even though they do believe that one day they will meet someone with whom they will spend the rest of their lives, and they also know, on some level, that this is not the person they are going to be with for the rest of their lives. That is my interpretation of "prolonging the doomed relationship." And that is definitely NOT a good idea!
The decision to live together should, in my opinion, be based ideally on two people who pretty much know, in their heart of hearts, that this is the One, and they are going to live together for a year before getting married more or less as a sort of formality, just crossing "t"s and dotting "i"s.
(That's basically what Mr Puff and I did. We essentially "knew" on our first date. We "went together" exclusively for about five years after that first date, then lived together for a year, and later this month, we will celebrate 11 years of marriage!
)
Now in the case of people who both know and acknowledge that they are not going to get married, whether to each other or anybody doesn't matter, as long as both are being honest with themselves and each other, and they decide to live together either for reasons of practicality or because they just want to, that is fine with me, too.
There are others who for whatever reasons, do not want a formalized, on paper marriage, the marriage is in their hearts, and according to their beliefs, not only does it not need, but it should not be, made into any sort of legal and/or religious event. Many couples do in fact, live happily together all their lives without getting married, so according to my beliefs, marriage
is in hearts, I personally don't think that in the cosmic scheme of things, it matters whether there are any papers or any religious rituals, therefore I have no problem with people whose hearts are married moving in together.
The key is honesty. With the other person, and with oneself. Just as with marriage itself, no one should either marry or set up housekeeping with someone, or especially have a baby, cherishing illusions and delusions that the other person will "change" as a result, or that it will act as any kind of healing salve or crazy glue to hold together a troubled relationship!