>

Depends on what you mean by "strained". If their romantic relationship is strained but not hopeless, and they can live together in peace and still feel happy about that, I don't see anything wrong with that. 
If the marriage is making them unhappy, then yes, get divorced, 100%. If the relationship starts getting toxic, if there's a lot of fighting and screaming and such, then yes, get divorced. But "strained" feels a bit mild, or at least like a very broad term.
I don't think its a black or white thing. There are stained relationships which still maintain civil and they are ones that are totally unhinged. 
There are also scenarios where it get unhinged when the parents are actually seperated and put the anger on the child. 
Its a situation where you should look individually at it. But I agree, that there should not put blame or burden on a child. Parents have to fill a role and put their individual needs behind. But there are so many factors which can influence the situation. >

There are bad co-parenting situations where the parents are separated, and there are okayish situations where the parents do their best to tolerate each other together, but I dont think theres many situations where staying together where, without kids, you would separate, ever actually improves things. >


but I dont think theres many situations where staying together where, without kids, you would separate, ever actually improves things.

It often comes with monetary situation, some people cant afford to support children and have two homes. But yes, in general its probably true. To still live together when otherwise being seperated you have to be very mature about the situation and that can be very hard when feelings are involved. >

Fair point about the financial aspect. If you're very poor and can manage to be respectful of your co-parent then staying together is probably the right call.