God: The supposed maker of the universe: An intellectually useless hypothesis, that for some is emotionally satisfying.
The mathematician Pierre Simon de La Place, who wrote a celestial mechanics, is supposed to have answered Napoleon, when he desired to know where God was in his system that described the movements of the heavens, 'I have no need for that hypothesis', and neither have I.
Many feel differently, but this feeling is rarely based on good arguments, and normally derives from wishful thinking and a religious education in childhood, when one could not defend oneself rationally.
In any case, I discuss religion and two standard arguments for God's existence, namely the Cosmological argument and the Design argument in this dictionary, and also discuss Pascal's Wager, and have myself the benefit of a non-religious education.
1. A little less seriously
There are also other arguments against the hypothesis of God, and I here give three of them.
First: God is a hypothesis, and not a fact, for all you know, whatever the depth or direction of your convictions. Even if He (She, It, They) exist(s), no one has succeeded in giving an argument for His existence that is logically sound: valid with true premisses. Moreover, all religious beliefs in a god or gods have come with lots of claims that since they were originally made - often more than a thousand years ago - have been shown to be either false or very improbable by science, indeed like much else that people long ago believed.
You may believe in a hypothesis, but as long as you have no uncontroversial logically sound proof for your beliefs you have no right to demand from others that they believe what you believe, nor do you have a right to demand their respect for your beliefs. You do have the right to believe what you please - but in fairness only if you allow others precisely the same right. Others may well believe that your beliefs are ridiculous, but then happily you may believe the same about their beliefs. And as long as you merely argue and not fight, such differences of opinion may even produce useful ideas.
Second: God is an intellectually useless hypothesis, like my belief in Santa, which for the moment I wallow in, because I wish to, and like to, and desire to. You may never even have heard of Santa, but - it may initially amaze you to learn - Santa made everything there is, including your god or gods, and you yourself, and me, and all the devils that ever were thought of by anyone, and anything else besides, for Santa is infinitely powerful and most mysterious and made all of the infinitely many universes anybody ever thought of. Verily!
How have I arrived at this most holy and beneficient knowledge of Santa? By a deeply religious process of reasoning, that has been followed by all the prophets of all the divinities, and that has been faithfully repeated by all priests and clergy. Here it is, all for your benefit and instruction:
Premiss 1: I cannot explain X.
Premiss 2: I wish to explain X.
Conclusion: Santa made X.
Note that this is a most satisfyingly simple process of reasoning: Why X? Santa made it! Why Y? Santa must have desired it! And don't you dare to disagree, for then you deeply offend my most holy and strongest feelings! Besides, Santa dislikes those who disbelieve in Santa, according to the best authorities on Santa, so if I were you I would take care, and beware of Santa! Maybe Santa, in His Infinite Goodness, fries doubters and scoffers like you for breakfast! Or what is almost as bad and far more probable: Maybe believers in Santa do!
Third: The God you believe in probably does not exist. He certainly does not exist if his existence implies a contradiction, as most divine hypotheses do, so suppose - a large and improbable hypothesis, but suppose! - your belief in your God is consistent. Is it true? Here is a premiss:
Premiss A: What a majority believes to be true probably is true.
This is a widely believed hypothesis. Suppose it is true. Since most men on earth do not believe in your god even if they believe in some god, your belief in your god is probably false.
Here I grant that historically by far the greatest part of mankind has believed in some god - and I insist that there have been very many different such beliefs that mutually contradict each other. Therefore the argument I gave is sound if you accept the premiss.
2. More seriously
So I am an unbeliever, and indeed not even an agnostic, not because I cannot see that the hypothesis of God is formally contingent, for which reason there may be a non-zero probability that it is true, but because there are lots of contingent hypotheses I also reject quite confidently, since there is no evidence for them, and lots of evidence against: There are no mermaids, no dragons, no griffons and no elfs either. Also, there is no Santa Claus, even if it would be nice if he were to exist.
The serious difficulty I have with most religions and most religious believers I know of is that they seem to be totalitarian at heart, even if they know well how to pretend tolerance if they are in a minority. Related difficulties I have are that the believers in religious faiths tend to be prone to insist that one should respect their faith, and that it is somehow moral to believe in some God, and immoral not to.
First, about "respect". I cannot understand why I should respect any belief or any person just because he happens to have a belief.
Of course, if the believers in it tell me they will kill me if I don't believe like they do - as believers in many religious faiths have done, which practice has killed millions of human beings simply because they believed other than those who therefore murdered them - it does make practical sense to pretend respect.
I can understand why religious believers demand or desire respect: Unlike mathematics or science, they have no plausible rational arguments for their religious beliefs. And religious beliefs are precisely the kind of belief that strike non-believers as patently false and at least a little ridiculous.
Second, about "morality". I do not see why it is moral to believe in some God. Indeed, being an atheist I believe that - if morals are involved - since it is more moral not to believe something for which there is no good evidence than to believe it, it is more moral not to believe in a God.
Read Clifford, and seriously consider in the present context Clifford's dictum:
"It is wrong always, everywhere, and for anyone, to believe anything upon insufficient evidence".
This also holds for all manner of religious beliefs.
Apart from my lack of faith and apart from Clifford: The evidence about morality and religion is very diverse. It is true that the fears of hell or the promises about the hereafter may have prevented some murder and mayhem that might have been committed otherwise. It is also true that literally millions of men, women and children of many faiths - Christian, Mohammedan, Hinduistic, Buddhistic etc. - have been killed by people of different faiths - Christian, Mohammedan, Hinduistic, Buddhistic etc. - simply because they had another faith.
In brief: Religious motives have been at the foundation of many acts that were quite bad by my moral norms, and also at the foundation of many acts that were quite good by my moral norms, and there just is no sensible pronouncement to the effect that religious belief is good or bad in moral consequences: The bookkeeping is too complicated and requires far too much detailed knowledge about motives, knowledge and ignorance, and much more.
But there is one important point here: One can agree about good and bad to a large extent without bringing in religious beliefs, and indeed one must do so as long as one does not want to start killing or persecuting others because they have another religious belief and do not want to give it up. One can agree in principle about morals because this requires only some minimal assumptions about human nature, that need no religious underpinning: That all human beings can be hurt and pleased in similar ways and have similar needs because they have similar constitutions.
Therefore, while I believe that there is no good evidence that the consequences of belief in some god or gods have been more good than bad on balance, I believe that there is excellent reason to try to settle one's moral differences peaceably and without demanding religious beliefs the people one must settle one's differences with do not share. For that carries no conviction and is bound to lead to problems.