Recently I have an discussion with my theist friend. But I don't think I have given him the best answer I can. There are some point I made I feel not comfortable with. But I don't know why. So I hope someone here can guide me to clear my thought. Friend: I need faith to believe in god as I need faith to believe my father is my biological father. I don't need blood test to confirm it. Me: In terms of logic, father is an entity who are with you since you were born. Whereas god is not. You have never seen god and there are no experiment available to prove god exist. In terms of morality, father is the one who take care of you and raise you. Blood-related is not important. But if you really care about it. You can still do the blood test.

Friend: My father contributed to my life. and it allowed me to come to this world. It shows father love children. Me: To contribute sperm alone is not an act of love. In Mainland China, people abandoned their child simply because it is not a boy. Some cult may make baby just for ritual. How can this be an act of love. Friend: There are so many reason for it.. End of discussion.

i kinda agree with you that you didn't give the best answer, because your friend is talking about personal experience and that you gave a general answer.

the respect towards a parent and god is separated into different expects looking at god as a father is for the spiritual side of things, a good in everyone for example. where as his/her father is just a good person

you should tell your friend that s/he is lucky then to have a good father, not everyone have good parents. because all over the world there are those who are born in an abusive family, some children are sold, some forced into child labor/prostitution and some loved.

This is an excellent example of why the more fantastical the claim, the larger the burden of proof. If you tell me your name is John, I am happy to accept your name is John until I am provided evidence otherwise. If you tell me you are the re-incarnation of John the Baptist, I am likely to disbelieve you outright. Can you see the difference there?

A paternity test would have little bearing on the relationship between your friend and his father. His father is likely to continue to treat him the same regardless of the results. The father's claim that he is the paternal father is not a very fantastical claim.

The claim that there is a benign, omnipotent, omniscient being is a fantastical claim.

Consider a friend tells you that he believes in fairies. He can not provide any evidence whatsoever because they only appear to him. You are likely to disbelieve him, but you are happy to allow him his delusion. A day later, your same friend approaches you and says the fairies told him that he needs to kill someone to appease them. Would you demand proof now? Would you require more proof now than you would when he just said he believed in fairies?

Most mainstream Christians may not be claiming god is telling them to kill people, but there are plenty that want to demonize certain 'sinners'. As rational people, is it not our responsibility to demand some kind of proof to validate their claims?