publications - Why publish in a journal instead of in arXiv or in my blog?

I don´t know what is exactly the value of publishing a high impact paper in a journal or magazine (electronic or not, open-access or not). I have several doubts about the benefits of publishing on a journal. Sorry for asking so many questions in the same post but separately it would result redundant.

Is it a question of money, pride, prestige?

Is not it better for humanity to be published in an open place accessible to all, in a simple language without such academic rigor?

If the reason is money, how much can I earn with a high impact paper?

If my publication shows new methods and algorithms that solve overwhelming problems that involve big costs for the pharmaceutical and aeronautical industry, can I claim copyright if they implement my methods and algorithms? Publishing in a journal is better in that case?

How could I prevent it from being used for destructive purposes?

Answer

I can answer a couple of your questions and may revise as I learn more.

If you publish something then in many places you have copyright already. Registration of the work may be required in some places and once was in the US, but no longer. Here, at least, if you publish something the copyright is yours and while your words can't be used without a license, your ideas can.

The way to protect "inventions" is through patent. This will almost always require registration (and cost), but is the only way to keep others from exploiting your ideas (as distinct from your words). But if I describe an idea that leads to a "process" or invention, but don't patent it, then others can exploit it freely. They might even try to patent it themselves, but you can (more money) probably prevent that.

One of the big problems for a researcher is gaining a reputation. This implies the need for your work to be seen by as many people as possible. Self publishing and writing a journal has the problem that it is difficult for people to find your work. Publishers, with all their problems, provide a partial cure for that, as do conference presentations.

Finally, for now, you are unlikely, in the absence of a patent and an implementation of the patent, to make very much money from publishing. The exceptions are textbooks for elementary economics or calculus courses, but only a few others. If you want to make money from publishing, write popular novels. (But "popular" is the hard part.)

One possible exception to the above, is that you can self publish successfully provided that nearly all of the people who would be your audience already know how to find you. If you have an already popular blog, for example, read by nearly everyone who cares, then you might be fine. But building audience is a hard task.

Disclaimer: I'm not a lawyer and the law varies widely around the world.