Dude... I don't want to discourage you from this kind of topic, but I totally disagree. This is just a ranting/venting session.
This doesn't just happen with gaming. It happened with politics, philosophy, coffee shops, schools, colleges/universities, etc. It's happened elsewhere, and it's happening now again, and it'll continue to happen.
This isn't a problem with the community or the game; it's a problem of the community moderation/administration of those games. In Minecraft, if you've got underaged gamers who are acting immaturely or annoyingly, you should report them. Or just leave, and go somewhere else. Find another server if you must. Make your own and get good moderators/admins to run it.
Make good rules, helpful guidelines, tips, ideas, tutorials, etc. Encourage good behavior in your community be rewarding it with positions of authority, featuring that person's content, etc. Give them some kind of encouragement, whatever it may be. Discourage bad behavior, and issue warnings or bans when appropriate. This is Community Management 101 for any type of online or gaming community.
This has happened with online games, because of the way online games work. Someone makes an account, that person pays money to buy the game or a subscription, and logs on. Anyone can do it, so when someone does, it's a 'russian roulette'/'dice throw' of what kind of member they are when the join that community. It can be bad or good, but if there are millions of users, you'll eventually end up with some bad apples - it's the consequence of being successful/popular.
If you don't like bad apples in your servers or games, don't play with them. If there are bad servers where the moderators or admins don't get it or don't do their job, and either can't or won't keep bad members out, then don't use those servers. If a game is online only and has a bad community, stop buying items on that game (including DLCs), stop playing it, cancel your subscription to it, and find somewhere else which doesn't have those problems. Vote with your wallet, if not for the sake of changing the world (even if only a bit), than just to keep yourself from the grief of being surrounded by users whose attitude isn't agreeable with you.
You'll find these issues anywhere and everywhere on the internet. The world is growing, and that means with more connectivity you're going to continue to connect with more and more people, and interact with them. If every stranger you find is a russian roulette of character and personality, and that randomness is part of the inherent diversity of humanity, than having bad apples is a side effect of living in a world where not everybody will be compatible with you.
You won't like everyone you meet online. Heck, you'll probably find more annoying people than you will find those who are helpful or pleasant. But you can either learn tolerance, or develop grief, and the choice is yours to make (because how you react is still a choice). You can continue to be around those who you actively dislike and/or despise, or you can try the russian roulette of communities and hope you find some other game or community which you like more.
It's the same with forums, people on social networks, clubs, bars, etc. Every community is the same way.
You'll never find a perfect community. You'll never find a perfect game. Because since we're people who are in a constant state of change, and our definition of "perfection" at any given time changes with us, than we'll continue to have an ever-changing definition of "perfection" - so we'll never be satisfied, and we'll never find "perfection" forever. We may find something "perfect" for a while, but as we change our minds and grow through the course of time, we'll grow dissatisfied with whatever we found to be "perfect" before.
It's life. It's humanity. We're all different. Not to make a cheesy movie quote, but "Life is like a box of chocolates. You never know what you're gonna get." So if by chance you should pick the toothpaste-filled truffle, spit it out and pick another chocolate; or don't, it's up to you. When you leave your door in the morning to go to work or school, I can assure you that there will be things that won't happen as planned, and that some of the things that'll happen to you are things you probably wouldn't have predicted on your own. That's because every time you wake up and leave your house, it's the roll of the dice, the draw of a card, a metaphorical russian roulette of chance and chaos.
You don't have to lament "the glorious days past" of PC Gaming. We're still in the beginning. Although some games may be filled with bad apples, there are many others just starting. Check out Space Engineers: it's Minecraft with Physics, but in space with stations and starships. Think of "Minecraft meets Star Citizen", but with good graphics and great physics (TheXPGamers on YouTube has some great speed builds of ships, and exdplains the game very well, go check 'em out!). It'll be online with multiplayer as well (and it's cheap on Steam as well, since it's still in beta), so you can try it out before it gets cluttered with bad apples and becomes the next Minecraft. Or you can make your own server, and moderate it yourself (so you can discover for yourself why moderating a community is so hard).
It's easy to say "the days of yore were better", but that is a statement which does nothing. You aren't really proposing a solution or saying what's wrong, nor are you doing anything about it. It's not a constructive argument, and it isn't helpful in changing anything.
If you want an idea for a better subject for your next blog post/topic/mini-article, how about telling/explaining to us what your ideas for "Good Gaming Community Rules and Better Gaming Community Guidelines" would be. Explain to us what's wrong right now with many communities, how to fix those issues, and why you chose your solution in particular. Give us alternatives, compare them with pros and cons of each alternative, defend your arguments, and give a conclusion of sorts to your work. Show us examples of good communities, show us examples of bad communities, explain what drives members away or what brings them somewhere, and how to keep an online community "healthy" and full of helpful, informative, kind users who treat each other well. You'd be surprised just how difficult that is - especially because creating and maintaining such a community is difficult, but doing that *and* keeping it active and growing at the same time is next to impossible.
It's easy to judge. It's easy to criticize. But coming up with a solution that works is extremely difficult. And pleasing everyone is next to impossible. So don't be so quick to jump to conclusions about this. Also, don't play those games which you know have immature members; don't play CoD, don't play WoW, don't play Minecraft. Try a good single-player game like Skyrim, Crysis, Metro:LL, Borderlands 2... or join an online game which isn't popular yet. Because you probably could have already solved this kind of problem if you really wanted to and had put your mind into it. There are many solutions, and many alternatives out there, and we've got Google to help you find solutions and alternatives if you want. It's up to you.