Although to be serious, if my child, knowing my opinion on matters such of these, were to do so, knowing my thought on the matter would be (WARNING: You may take it as offensive) "You've chosen a fictional, made-up entity over your own father," then he/she would know I would lose a lot of the familial bond we would have, would know how insulted I would be and how hurt I would be, and was doing all those things to me willingly.
And then I'm to be branded as selfish?
Do you actually have any kids?
If so, is your trust in their judgment really so little that if they came to you and said, "Dad, I know you don't believe this way, but I've had these experiences which lead me to believe there is a God", you would dismiss it out of hand? Without even allowing for ANY possibility that they could be doing what's right for them?
Oh, and yes, you would rightfully be branded as selfish if you reacted that way.