That's a legal question and the answer in most countries is - they can't do that. From non-legal side - people don't have the same expectation from marriage and friendship.
Well, according to my question they live in a country where they can :)
And, no, this was not a legal question at all. Can you pinpoint what exactly makes the expectation of friendship and marriage different in this context? Assume both people have full-time jobs, both take care of children the same amount of time, etc.
I don't think this is a honest philosophical question. First you need to define what you are talking about, specifically what you define as marriage and friendship if you're taking edge cases of being in a country without legal marriage protections and insinuating that friends are raising kids together. I think the other person's interpretation that you are trolling is more believable than your claim. This could change if you are able to articulate your argument (whatever that might be).
But the legality aspect doesn't matter in this case. It's about the friendship/marriage and how you feel about yourself and the other under these circumstances. It's possible in some countries to be married and not share wealth, but if it weren't you could consider it purely hypothetical. With the question I asked, I wanted to evoke philosophical curiosity. Even the great Greek philosophers ruminated about what it means to be friends versus married, so it must be an interesting topic, and certainly when combined with the topic of this post. And if you wonder about my "definitions", just assume that they are as diametrically opposed to your view as possible, to make an interesting conversation.
And, no, this was not a legal question at all. Can you pinpoint what exactly makes the expectation of friendship and marriage different in this context? Assume both people have full-time jobs, both take care of children the same amount of time, etc.