Old is out New is in?

What is it about the old testament that makes it so desirable for people to want to write off the content as if it doesn't matter anymore. So, someone says, "but that's the old testament". What is it that Christians really saying? Well, maybe recognizing that there's a difference between the old testament and new testament. But, that's not about differences, perhaps "exceptions" what God's like in each of the two sections of your holy book. But, if you are recognizing the problems and drawing the line and trying to argue that one of these is no longer relevant or should be dismissed. My question that comes to my mind is.

1.  Why should there be a problem at all? When the view is that this is something that God has revealed to humanity that the old testament includes important messages or included messages that were important to people for thousands and thousands of years, what is it that change?
2.  What is it that is new and relevant?
3.  Why does it supersede or after what came before?
4.  Did God's character change in between two testaments?
5.  Did the rules change?
6.  Did morality change?
7.  Did our understanding of the universe change?
8.  What exactly is it that Christians trying to describe and quite often there is no explanation except self-interpretation or it seems more of a kind of cherry-picking? Oh yes, that verse seems uncomfortable and so I will just dismiss it as this is the old testament and Jesus came along better and later made everything better and new.
9.  What reasons do they give for these disparities exists? Well, perhaps flawed nature of human beings where God's communicating a message but maybe we write it down wrong. Or Christians don't understand it correctly. But, if that's the case the wouldn't this also be true for all the new testament.
10. If the problem is having difficulty communicating with his creation, how do you know that he's not still having to communicate with his creation?
11. Why do you get to disregard the old testament?
12. How do you know that the new testament is any less flawed? What your other interpretations to resolve this problem to fit every Christian. An introduction and there are two theological responses for the need. One is covenant theology and the other is dispensationalism. Most Christians I know are fit in the second theological responses.

Yes, I'm pointing out the problems, issues, and contradictions. What I am understanding from your views that it comes from God.