firstly I think you need to understand that there is a lot to gain. Look at his legacy after death and those of his direct followers. I mean lets be seriousSo he decided where he would be born and whom he would be a descendant of? Do you realize how many prophesies there were regarding his ancestry, birth, ministry, death burial and resurrection? If you did, I don't think you would really pose that argument.
Besides, what would one have to gain even if this ruse was possible? No wealth, no women, torture and finally crucification.
And what of His followers who Proclaimed to be eye witnesses of the resurrected Christ? What did they have to gain for lying? Every one of his disciples were martyred. A man might die for something he believes to be true but certainly not for something he knows to be a lie.
Also, you need to understand the importance of pagan beliefs here. There are many ties from the origins of christianity (son of god and virgin birth) in other beliefs. It just makes you wonder