First as mentioned sunlight is good for you, so is fresh air, even without taking into account the fact you may have mold etc in your home that builds up over time (that can happen even if you do go out regularly).
Going out also gets you into contact with germs etc, which may seem bad (and can be) but if you rarely go out, you don't develop any sort of resistance and when you do get something, it can be really bad.
Mentally going out, even if you don't socialize, gives you new forms of stimulation mentally, being in the same place every day, constantly, even with plenty to do can be bad for mental health. This is one reason they even allow inmates to get outside for an hour a day etc. Long term effects could be hard, including the inabbility to go out at all eventually (more and more likely to just stay inside from then on).
The social part is important as well, but you could have people come over and visit you etc, so you can get around that. Still, not interacting with people tends to snowball, and often if you don't interact with others for long enough, it again becomes harder and harder to do so.
Can you live in your house, by yourself, and survive for decades? Sure!! With plenty of Video games, good books, TV/internet and lots of yummy food delivered you can even do it by yourself and still be somewhat happy.
I would suggest that even minor excursions out though, even if it's just to go eat somewhere, or run to stores to buy things directly etc, will improve your life, make you happier with what you do have, and keep your options open.
You can......suppliment your health with Vitamins if you don't get enough sunlight, and honestly you can socialize through the internet/headphones and video games at this point (possibly easier and more enjoyable for some then real life socialization. If VR improves eventually people may often not end up going out almost at all (I mean look at how many communicate mainly with Cell phones at this point...often even if in the same room!!).
Real human physical contact though, or even being in the same room, watching a show together, playing a board game, eating a meal, those are all food for your soul, and a much more filling one then you can get online, or through VR, at least for now.
Who knows what the future holds though (The shadow probably).
Ok, you made some very good points.
I'm already at the point where I don't want to go outside unless I have to. I have to figure out what I can do outside of my home.
Oh and I take Vitamin D. I know it's not the same as taking Vitamin D straight from the sunlight, but it's better than nothing I suppose. ---