Okay, so this isn't my thread but I'm an agnostic Atheist so I'm going to throw in my 2c and supply some answers.
DO I BELIEVE IN GOOD AND BAD?
Tough question. I don't believe Good and Evil exist as entities in their own right. They are labels we apply to things in the world, primarily the actions of people.
To some extent, these definitions are variable. A gay person who considers his relationship very good may be branded evil by someone else. A lot of things are very hard to ethically define, topics like the death penalty or euthinasia. There are no cut and dry, easy definitions for things like this. They require a lot of thought.
As a general rule, do unto others as you would have done unto yourself is a decent and fairly universal benchmark. Few people on earth would disagree that trying to kill a baby is bad and that trying to save one is good.
WHY DO'NT I BELIEVE IN GOD?
Primarily, lack of evidence. God may exist. I don't know. But I find it illogical to believe in something when I see no evidence of it's existance. The more specific the definition of God, the less credible I seem to find him. To me, religions simply take the ideas and prejudices of mankind and label them God.
HOW CAN SO MANY PEOPLE MAKE UP RELIGIONS AND HAVE SO MANY PEOPLE FOLLOW THEM?
I don't see why this question is targeted to an atheist specifically. After all, even theists tend to believe that every other religion but there's is wrong. People like to belong. They like to have answers, especially to questions with massive scope (where did we come from, what happens when we die). With a few exceptions (such as, in my opinion Mormonism and Scientology) religions don't start by someone just making something up and people believing it. Religions develop over a long time, entwining with a culture and the way it develops.
Personally, from a science angle, I believe that humans are predisposed to religious and supernatural believe due to a convergence of evolutionary adaptations: Pattern recognition, speculative thought and a desire for answers.
HAVE A TRIED LOOKING INTO OTHER RELIGIONS?
Not especially. I do try and find out what I can about different belief systems. I'm an infojunkie. But none of them seem any more credible than the other. While some contain tenants that make sense to me the justification for these tenants (a supernatural source) rings false to me. If anything the sheer number of religions in the world makes all of them less creidble. Humans seek answers and where they cannot find them, they will invent them.
ADDITION:
For the record, I have been an agnostic atheist as long as I remember. While I remmebr bible stories from my youth, I never considered them any more real than Norse or Greek myths, which I also liked.
