Hmmm I see both sides of this argument. I was married almost three years ago, we've been together almost 15. To be fair I don't feel more protected but then I always had enough trust in him that if things went tits up he wouldn't try and fleece me.
I don't like being called "Mrs" - just because it makes me feel old
and I'm still not entirely happy about taking his name (I did because it was important to him but I feel like I've borrowed somebody else's and it's not really my name).
"What's your name?" "it's err...". I still have to think about what my bloody name is!
The biggest committment you'll ever make to somebody is to have a child with them. Marriages can be dissolved, no kids involved then you're both free to walk away and never have another thng to do with them. Kids? well, you've got a permanent bond haven't you?
I think having children with somebody makes it clear enough there is (or at least has been) a sexual relationship and can't be passed off as "the lodger".
Maybe put something in place for co-habiteess who have children? alernatively don't live with somebody who you even remotely suspect would be capable of taking you to the cleaners if it all goes wrong.