1) Prayer to Biblegod doesn't work. This is the conclusion from numerous studies conducted in the Western world on the subject of prayer.
2) The widespread lack of agreement among Christians on basic aspects of the faith suggests their faith is not divinely inspired (a genuine God would have been capable of communicating his truth effectively);
3) The sordid and violent history of Christendom suggests the faith does not work;
4) The mass of evidence showing that early Christians were prolific liars and forgers on behalf of their messiah;
5) The mass of evidence showing the Resurrection is not a genuine historical event, but rather, the product of delusions, deceptions and wishful thinking.
These are the five points that convinced me Christianity is false, but I would be interested in hearing what others think. What are the main points that convinced you Christianity is a con?
[edited to add: I really should add another point to the list, which is:
6) The hundreds of contradictions, errors and logical impossibilities found in the New Testament.]