Gospel Contradictions

If Christianity is one big conspiracy, we wouldn't find so many mistakes and inconsistencies in the Gospels! Surely if the faith was one big lie, the Gospels would have some uniformity to them, united to deceive readers.

Well, that's one side of the argument. Others might point to the Gospel contradictions as proof the entire thing is made up.

So, why are there contradictions in the Gospels? Does this undermine their credibility?