Second, you said that certain beliefs were "idiotic," and these are beliefs held in common by many Christians. quote]
true christianity would not include manmade doctrines
First,
Who are you to define what "true Christianity" is? Who appointed you Decider of Who and What Is in the Fold?
Second,
Perhaps you should take your own statement to heart and take a good long look at your own religion. EVERY church has beliefs and they are all humanity's attempt to understand the Bible and the spiritual experience.
A Christianity without any manmade doctrines/beliefs would be a Christianity without pastors, without sermons, without discussion. Each person would just read their Bible and interpret it as best they could and there would be no need for group study. The reason we have the group effort is that the Bible was not written like a computer instruction manual or a chemistry textbook. There is a lot that needs to be interpreted and experienced to be understood, and so it isn't surprising that people try to help one another and share their thoughts on it. The JWs have one of these interpretations. The Catholics have one. All denominations have one, and in fact, most solitary practitioners and non-churchgoers still form their interpretations.
It is what humans do. We read something that is complex, and we try to apply it to our lives and that means we interpret it.
No one has a Christianity devoid of doctrine/belief, unless they don't bother to believe in anything at all, outside of following Christ's example.
The JWs have a TON of doctrines/beliefs. I know, because they've sat in my living room before and we've had long discussions about them.
I suppose you think the JWs got their beliefs/doctrines straight from God, but I say... yeah, you say that and about a dozen other groups that have told me the same thing. How can you show that you're any different than these other groups that say they have The Way. I prefer to know when and how each doctrine came about, so I can reflect on the Bible and compare the two, and decide for myself if it is an appropriate belief or not. I don't do well with someone telling me they have the answer, and on closer questioning, they don't and they don't even know where their beliefs came from.