We see things for what they are, not for what some higher power makes it out to be.
I don't need a book, or a chest of stone tablets to give me good guidelines for life. I am human, and with that comes conscience.
The most obvious reason as to why Christianity is bullsh*t, is because the stupidest things have happened in the name of it.
A pointless series of wars, that lead to suffering of thousands. It went back and forth over hundreds of years, always coming to a standstill. Yet the Pope kept insisting, so they kept going back.
Most of you have probably never heard of the Childrens' Crusade. This was a forced march of over 10,000 children, most not even teenagers. By the time they arrived in the Holy Land, they were so weak and malnourished, that the Arabs slaughtered them all. They thought faith would protect them, yet it did not.
The Spanish Inquisition
This is when Christian "Inquisitors" went from house to house, determining people's faith. If they didn't meet standards, they were executed. Not to mention, corrupt clergy used this as a chance to get rid of their enemies.
The Slaughter of the Knights Templar
This pisses me off more than anything, as this is quite possibly the most horrible thing Christianity has to answer for. The Knights Templar were essentially the Holy warriors of the Crusades. After countless years of service, they were repaid by being murdered and tortured by none other than fellow Christians. If I spent years in service to God, only to be attacked by God's servants, I would drop that faith immediately.