I see nothing wrong with a couple who intends on marrying to start living together.
My boyfriend and I have been together for 4 years. We are clearly getting ready for an engagement. In our minds, it's 100% set that we are getting married.
But, we are traditional. He wants to propose (as it's a right of passage for a man) and I want the proposal and ring. So, we are just gearing up for that.
But, we are starting to look around at places to rent for now. We definetely see ourselves moving in together within the next year. I would like to be engaged first. But, if we aren't at that point, it's OK. I know it's coming, because we've had that conversation.
I think if a couple is 100% set on being together in the future, I see nothing wrong with living together before marriage.
But, I do agree that it's a bit stupid that two people, with no future plans to marry, to start living together.
I don't even care about what their future spouse has to say. Things are spouses/future spouses have done in the past, should be left in the past. No need to feel threatened by something that happen before you came along. But, it's got to be a messy situation once they break up. Who keeps what and such.