Jesus freaking christ on a pogo-stick, OP. So many paragraphs give me a headache.
Anyway, yeah. I do think being a man-child is a bad thing, and that's coming from a self-confessed man-child who is a 21 year old virgin that has absolutely zero self-reliance skills. I can't cook. I can't clean, iron, i don't know what APR stands for and i have no sodding idea how to pay taxes. I feel, well, completely and utterly useless. When i hit 18 i expected to have taken some magical pill that will suddenly make me into the self-reliant drone that knows all this adult stuff without any form of education beforehand. Now that i'm 21, it's outright expected that i know it all by now and... i don't. I'm actually terrified of life by myself because i know i'm going to be so fucking incompetant and screw it all up. I'm going to be living off pot noodles for the rest of my life.
I know why this is the case, though. Growing up i've had it incredibly easy. My parents father has an impressive income that meant anything that was wanted or needed, i got. I essentially became the spoilt brat - a statement that holds up as even more true when you consider the fact i'm an only child. Now i'm all grown up, i should be looking out for myself. But the fact is i'm still playing games all day long while studying university courses in the comfort of my own home, with things provided to me and meals cooked for me. I live like a king in some respects, and i'm scared to have that status quo change. It's not just fear of an inferior life; it's the thought that when it comes down to it i just won't be able to look after myself.
I really think people should place a higher value on independence and future parents should heed my tale of becoming entirely dependent on a caregiver and try to teach their offspring the values of being able to maintain a relatively normal lifestyle. School doesn't teach you how to budget, how mortgage or insurance works or how to cook a meal that is little more than a microwavable packet and i really think this is a huge flaw in the education system, personally. I know you're supposed to learn all that shit when you move out to stay on campus for university but not everyone has that luxury.
Also OP i would argue you're looking at two different definitions of man-children. There's the irresponsible one (that's me) and there's the cultural one. The one that watches My Little Pony and cartoon episodes of Transformers. In some people's eyes, man-children are the "excessively nerdy" type who still get excited about comic books and tabletop figurines at the age of 25+. If we're talking about the cultural aspect of man-children, i'd have to say that while reading comic books as a fully grown adult is a little bit strange, it's not hurting anyone so people should be free to embrace whatever aspect of cultures they enjoy. So what if adults like watching kids' shows? As long as it doesn't directly impact YOU, they can be as much a "man-child" as they damn well want to and my personal opinion shouldn't damn well impact that. That being said, it doesn't mean that i have to agree with it on a personal level, but rather respect the choices of those that do so.