Pascal's argument begins on the very uncontroversial premise that we do not know, without doubt, whether God exists or not. Therefore, we must choose between belief and non-belief because we do not know for certain. As Pascal says:
'You must wager. It is not optional. Which will you choose then? Let us estimate these two chances. If you gain, you gain all, if you lose, you lose nothing.'Pascal acknowledges this is an odd reason to believe, but with foresight, responds to his critics that God will know the difference between an opportunistic and a true believer. His response is that committed opportunists eventually condition themselves into true belief.
'Follow the way they began, by acting as if they believe, taking the holy water, having more masses said, etc. Even this will naturally make you believe and deaden acuteness.'
His argument can be summarised as followed. Once you have converted yourself, you will reap all the rewards of belief, provided you are right; an afterlife in Heaven in eternal pleasure etc. If you are wrong, you lose nothing but what Pascal dismisses as parasitic pleasures, like the television you watch on sunday morning. On the other hand, if you don't believe, and you are wrong, you are sentenced to eternal damnation in the fiery pits of hell. In short, it's safer to believe than not to believe. You might as well just believe.
However, Pacal's argument only takes into account private utility; private advantages and disadvantages. In doing so, he makes a fatal error; treating religion as a private personal thing rather than an institution across society. In order to truly assess the wager, we need to take into account the societal advantages of disbelief and the disadvantages of belief.
For example, dissenting thought from religion, and not believing, has brought huge gains to society. Ideas from thinkers such as Frederick Nietzche and Karl Marx were the result of dissenting from religion. The questioning of religious doctrine has brought us many scientific ideas, such as evolution. While the personal benefits of disbelief may be negligible, the societal gains can be significant. Therefore Pascal's wager becomes much less of a one-sided no brainer, and more of a value judgement. A judgement where somebody decides which is more important, their prospects, or society's prospects. Am I willing to risk eternal damnation instead of eternal bliss, for these advantages to society?
Religion also has negative effects that we can take into account. I don't mean to argue that religion is bad, just some aspects of it are. Religion does have good effects on society, but for brevity I shall play devil's advocate in response to Pascal's one sided gambit, and ignore these. One need only look at the endless wars, murders and morally abhorrent things committed in the name of religion to see the negative effects it can have on society. Religion could provide eternal bliss for believers, but if this belief causes people to act badly, the disadvantages to future generations and living conditions could outweigh these individual benefits.
Pascal's view of religion as it effects the individual is too narrow for the wager to be accurate. Religion has many effects on society and future generations, which should also be taken into account. However, once you do this, it becomes less one-sided.
There is another problem with Pascal's narrow view in that it does not account for the occurrence of many different religions in society, each with their own version of god. You either have to know which god is correct, in which case the wager is invalid because it is about acting in the face of uncertainty, or you have to guess which god is correct. In this instance, the wager loses it's effectiveness because your risk of going to hell, even if you believe in a god, increases. You're more likely to pick the wrong god, if any of the religions have got it right. There is an episode of the Simpsons where Homer Simpson, of all people, elegantly expresses this sentiment:
"Suppose we've chosen the wrong god. Every time we go to church, we're just making him madder and madder!"
If even Homer Simpson can point out flaws, Pascal has a problem.