You can play with flight sim games like MS Flight Simulator 2000 all you want but that really doesn't do much to help you learn how to fly a real plane. It can help in some things like navigation but a real plane has a completely different feel from a computer game. Real planes don't have you control critical systems with a keyboard, either.

Likewise, those "how to build an atomic bomb" sites aren't very useful unless you have a ready source of U235 or weapons grade plutonium. Postings like "12 easy steps to take over the world" would perhaps be believable if someone actually tried it to see if it worked.

The training available on the Net is only as good as the source material. Some of the Internet based classes probably have very good material. A person could learn a great deal using those resources. The key thing anyone needs when using the Internet is a good "BS filter" to help remove the crap from the substance. You can find all sorts of BS on the net, from alien ruins on the moon and Mars to kook conspiracy theories of every delusion imaginable.