Religions seem to constantly remind us of our failings and ineptitude. Christianity in particular bases itself around the fact that we are so rotten God had to sacrifice his only son (why did he only have one, he's omnipotent he could have as many as he bloody well likes) to save us from all the evil we are. Religion seems to preach and view humanity in a constant state of hopeless failure and evil which only God can free us from (then why doesn't he?). This message is so strong that when God does create himself in human form he is so overpowered by our destructive tendencies that he battles against temptation and even looses his temper and starts attacking people and smashing things up (Matthew 21:12-13; Mark 11:15-18; John 2:13-22). Though that's not to say as God himself he wasn't prone to a bit of cruelty and violence in his time.
The effect of religion to suck all hope from us cannot be understated, thousands of years of indoctrination have taught us that we are failures and disappointments to God. Though how can we disappoint God? God created us and is omniscient so being our creator he knew exactly how we'd turn out. How can the flawless God design something that would disappoint Him because of its flaws? It is impossible for us to disappoint or fail God because He made us that way. If he is a little peeved by our behaviour then it's his own fault: what did he expect? He saw it coming after all!
Jesus being apparent pure good (though by today's standards his acts aren't as loving and kind as you'd think) is also a huge psychological barrier. First we are told we cannot be good then we are given an example of what pure goodness is (free of sin) and are told that we cannot compare to it.
Religion seems bent on putting humanity down claiming that there cannot be true morality without God, which is to say humans are incapable of knowing good without God (to the extent that a rejection of God is a rejection of all that is good and only through God can good things be done). All of these aspects of the religious doctrine are hugely pessimistic and modern psychology is only too aware of the effects of behaviours on those bought up in a pessimistic environment: the child who is constantly told they will fail is likely to fail. If the Bible is God's word and it is from the Bible all this pessimism spouts is it that God actually wants us to fail?
If religion is there to save us from ourselves and the horrors we cause then why have we left a trail of historical atrocities behind us despite our strength of religious conviction? If God and His goodness have existed before man then why has the continued worship and following of His guidance borne our history?
Religions greatest trick has been to boast that without God there is no morality and without God we descend into a moral vacuum. Not only is this a big fact lie but another self fulfilling prophecy as culturally we start to accept that without religion we are lost to evil and therefore we succumb to it. The religious point to the state of the modern world as constant evidence of this fact yet they seem to neglect the many stories in the Bible of such awful societies of depraved and evil beings that God's hand is forced and he either carries out or orders their destruction (he rather enjoys this work and does it a lot). So if we us modern humans are so dreadful and far off the good path why has there been a distinct lack of righteous Biblical genocide (you will find few who would claim our modern equivalents are the works of God)?
We have to reclaim goodness as a human right and a natural human condition as strongly as the religious claim evil to be one. We are capable of being good and pure, beyond Christlike (after all isn't Dostoevsky's's Prince Myshkin more than believable or Gandhi as pure as Christ?). We are capable of goodness, despite what religion says we can aspire and work to become morally pure. This is a concept which hasn't passed Buddhists or Hindus by but only by shedding these ridiculous indoctrinations of our moral limitations which have seeped and corrupted into our cultures and conditioned us since birth do we have the slightest chance. We may even fail at first to achieve this but already we will be better than we are.
For a more coherent version of these ideas see Humanity: God's Little Disappointment