Hey man, being an atheist myself, having mostly atheist friends and family - allow me challange you on a few points:

it’s impossible to be one. Why? Because people don’t know everything about the universe.

This point could be valid if you judged all non-empirical-fact-based belief systems to have the same inherit flaw. Including every single type of theism. Man does not know everything but he has every right to have beliefs, even baseless ridiculous ones.

Also - one may argue that atheism is based, all of the atheists I know have never seen any proof for the kind of God that is described by the various types of theisms, they also have never seen any proof of the giant flying spaghetti monster - so they won't believe that either, even if they stumble on a book which is said to have been written by the spaghetti itself.

also making sure they define that higher power within ultra tight parameters to suit their belief system (i.e. ‘fairy in the sky’)

How else could you articles a sentence in which you try to explain what it is that you do not believe in? You have to be specific about what you don't believe.

In my definition of the term an atheist doesn't need to be believe that there's nothing after death, and no God watching our every step. But rather to not accept the theist view point. I've met very few people that believed with conviction that life is a meaningless mistake and all, but they were in an odd time in their life and it wasn't a perspective they held for long. I believe the technical term for people who hold no conviction for the nature of life and existence (rather than belief in the fatalistic absent of greater powers regardless of their nature) is non-theist. Is that you're point though? That we mistakenly call non-theists - atheists?

And why does the atheist more indoctrinated than the theist?

What's multitheism? Do you mean polytheism?