A friend of mine recently purchased a house with his girlfriend who will most likely marry, and while I don't think anyone has a moral problem with it there's very definitely a sentiment of "who the hell does that?" floating around. Even though things will be fine in all likelihood, if they were to break up I couldn't fault anyone (especially a potential future partner) for questioning their competency in long term decision making and priority setting afterwards. In that sense I get Link's point, though I don't see how something so impermanent as modern marriage would somehow make this scenario "better."
I understand the desire to erase these stigmas, yet who among you would enter a relationship with a single parent fresh out of some other dude/dudette's house with the same optimism as a relationship with a single, childless and financially independent person?
E: To be clear, I take no issue with cohabitation, but it doesn't shock or SCARE (wtf?) me that there are people that take it into heavier consideration when evaluating someone's personal responsibility and whether or not they'd like to take on any of it.
I have no problem with people cohabitating and if I were in a relationship that lasted at least a year or so I'd be open to getting an apartment with her. But I'm not cosigning any kind of mortgage unless I want to put a ring on it. A friend of mine is in the process of buying a house with someone they're dating who seems very flaky/noncomittal about the whole thing and it sounds like a disaster waiting to happen in my opinion.