i don't really follow the logic. i grew up with 2 parents and didn't get lost in a lesser role. i was a child, of course, but still a human being. i don't think its entirely healthy for a child to be in a purely 'friend' role with the parent, as aposed to the regular parent-child one, depending upon what that entails.
as a child i was spoken to on a level i could handle, by two different adult parent people with different perspectives, skill sets, interests, personalities, who were in a relationship together. i also interacted regularly with a much bigger group of family members and extended family- their adult friends and collegues.
i think i benefited from this- i learned early on that people are all different, and learned a lot from watching them problem-solve and discuss and argue and negotiate, i didn't feel shoved from pillar to post, or like i missed a level of intimacy because there were more than 2 people in our relationship (i have a brother and a half brother too, so at some points there were 5 of us).
i get that you feel a close bond with your father as the primary parental figure in your childhood- thats great. but i think you've made a big old sweeping statement that imples your experience is everyones experience, and that what worked out well for you means a superior outcome for everyone else being raised by a single parent- when thats not the case. my bf raised a daughter alone, and while he did a great job, and they're close, she feels something was missing, personally, she envies her cousins who had brothers and sisters and a mother in their life.
i think traditionally families were seen as ideally having a male and female parent, because traditional gender roles made it work pretty well like that- and the gender role debate aside, i do think men and women tend to think relatively differently and use different approaches for the mostpart, and seeing this doesn't hurt a childs development. its also arguably easier to raise a kid logistically and financially when you're not shouldering all of the workload. 2 parent families were probably also pushed by religious groups and the like to try and keep people functioning how they wanted us too. and blah blah blah.
that said, i (as a person, but not answering on behalf of all people) don't think decency (however we're defining it) is dependant on 2 live-in parents- one of either gender, any more than it is dependant on myriad other factors.