Why do talks on religons go sour?
I think the real problem here is that you're trying to prove something to someone who doesn't have the willingness to learn. The person doesn't believe for a reason, The reason may not be a good one for you but it certainly is for them. Whatever their reason is you should first hear them out on it fully. You should be patient and take interest in what they are saying as it is what they believe.
You believe in something and would want the respect given to you by another so the thing to do is to hear them out. Listen to what they say and then when they have felt that they have said all then thank them for sharing that with you. They will be much more receptive to what you have to say afterwards since they have already said their peace, their attention would come off them and onto you.
Their interest for you will increase and they will be more likely to listen to what you have to say. The thing to not do is make them wrong for what they believe so be careful. This is probably a major point here in most religious arguments is that the people talking on this subject usually verbally attack one another and make the other person wrong for what they believe.
In the past people have tried to use force to get others to believe something else and it may seem to work temporary but in the long run it ends up backfiring on the enforcer. This has been seen down the ages and is something that repeats throughout history. Force never works in the long run.
The best thing to do is respect their belief, Even if is very opposite yours. Respect and agree are two different things. We all have the freedom to believe whatever we want and due to one's own experiences each person will believe what they have experienced. What is funny is that sometimes a person will realize that they have had an experience that was beyond normal explanation and realize that there may be "something more" out there.
Even if not you can share your beliefs with them and maybe you can find a middle ground with them that might open the door to them finding "the light switch."