I have heard plenty of arguments for the existence of God and not a single one works. Let's see if I can avoid ranting or drag on in explaining them.
The most recent one to be brought in front of me was the argument of the egotistical or faith-filled atheist. It claims that being an atheist requires just as much faith as being religious. This is silly. We don't claim to know everything. We, in actuality, claim to know much less then religious people do. We don't know how the world began. We don't know where humans came from. We don't know what happens after we die.
We have ideas of how these things work. Ideas based off of reality and I'd rather take ideas over the rantings in a 2000 year old book any day.
It's the relation between facts, theories and hypotheses that most people who make this argument don't understand. Evolution happening is fact. How evolution works is a theory. The thought that the Earth hasn't always been here is fact. The big bang theory is a theory.
As for hypotheses...A hypothesis is an idea that has nothing to back it up. It can become a theory after that and, in some cases, even become a fact.
Christianity is a hypothesis. It has nothing to support it and many proofs against in. In science, if you find proof against a hypothesis, you abandon it and find another one. In religion, you call it faith and ignore all the reality that proves your beliefs wrong.
Another silly argument I hear often says 'Love/Morality/Life/Happiness/Etc. comes from God. Without God there is no (your above choice).' Also, in my opinion, without the existence of Poseidon the ocean doesn't exist.
Attaching your baseless deity to an emotion or behavior doesn't make it exist. Popsicles can't exist without God. Well, since popsicles exist, God must as well. There is no logical application of this argument.
The above behaviors exist within humans simply because, as humans we are social creatures, we can feel pain and like to avoid it, and we have the cognitive ability to notice the emotions and reactions of other humans. Since we don't enjoy pain we assume, quite correctly, that others people don't enjoy pain either. Empathy is natural for a social creature who thrives off of emotional bonds.
Evolutionarily it's simple to realize that a human who works against other humans is less likely to survive than one who does work with others. Fending off predators, gathering food, raising one's young, and improving technology and culture are all things that easily work better with help from others. In common day it is obvious why most people live in cities and towns instead of alone in the wilderness. It is easier to trade labor for money and the money for shelter and food than to build your own shelter and gather your own food.
Assuming you are going to live in these societies, not killing and stealing from others works best. You would prefer no one else would perform these actions on you so, with fingers crossed, you don't do it to them hoping they do the same for you. In fact, though there is always deviants, most people conform to the standards.
This is where laws come from, really. People prefer to not be attacked by others in society. Society flows better when you follow the laws of the society. To be part of the society you follow these rules.
Maybe I'm a rare case, but I have no interest in stealing or killing. It isn't from fear of retaliation from society via fines or imprisonment. It isn't fear of going to hell after I die. It is simply because I don't want to be stolen from. I don't want to be killed. I respect other people's right to life and property. I don't think they deserve to be hurt if they aren't hurting anyone else.
An interesting thing, in relation to this post is the Surrogate Mother Experiment by Harry Harlow. In this experiment baby monkeys were put in a cage with two fake mothers one made of terrycloth and the other made of wire. Even if the wire mother was the source of food, it was shown that the baby monkeys went to the terrycloth mother if a threat was introduced. Food source didn't matter. All that mattered was the source of comfort. Other humans are a source of comfort. Even without a god existing, we would still seek the comfort of other humans.
Any arguments for God I missed you would like me to disprove? Any ultimate proof of God I missed? Feel free to post it. I will believe in a god if you can provide proof for one. Of course, I mean relevant proof that can't point to anything besides a god.
A 2000 year old book could be proof of a god, or it could be proof that people wrote their beliefs down 2000 years ago. The platypus could be proof of god, or it could be proof of the common ancestry of mammals and birds. The 'finely tuned for life' universe we live in could be proof of god, or it could be proof of chance and the fact that if the laws of the universe weren't as they are, we wouldn't be here.