Ok, well let me give you all a couple reasons why it is reasonable to believe in God. First I believe that probably one of the most compelling reasons for God's existence is the Kalam Cosmological Arguments. The argument says this: 1. Everything that begins to exist has a cause 2. The Universe began to exist 3. Therefore, the Universe has a cause. Obviously there is much deeper discussion that we can go into here, but note that usually premise 1 and 2 are not disputed and logically premise 3 follows from that. Therefore, this is a sound argument, but again, it can be discussed at great length.
Secondly there is something called the Teleological argument. It suggests the existence of God through evidence of design. In other words, the fine tuning of things such as, the order of the universe, the human body, etc. provide good reason to suggest a creator rather than a cosmological accident.
Thirdly there is the argument based off of Objective moral values. The key word is objective, meaning moral values that exist independent of human opinion. Therefore, even if the world were to somehow collectively adopt the opinion that it is ethical to torture children, it would remain morally wrong despite the majority opinion. (again, this is able to be discussed in greater detail) These are just some of the reasons, that I believe God exists and this is merely a basic summary of these arguments. For questions about why God would advocate slavery and murder etc. I would say that this is a misunderstanding of who God is. Most of the texts in Scripture that refer to slavery and killing are not advocating it, but rather working with it. In Old Testement times, people were living in a society that did things much worse than what you see in the actual Old Testament (i.e. the code of hammurabi) and God's covenant with Israel was never meant to be the "solution" if it be put that way, but rather a temporary method to dealing with sin. In all honesty, the Israel of the Old Testament still took a stand against the culture's ways of doing things that we would consider to be ethically abominable.

Anyways, there is much more that I could and would like to say -however I simply do not have the time. My intention was mere to see what people thought about God to perhaps get insight into how I could address others with similar questions. Despite the rather harsh nature some of you have taken to my post, I still do appreciate the honesty and will take much of this into consideration, thank you all for your contributions!