First of all who is to determine which part of the religion is true and good and which part should be discarded? Can anyone make that judgment on his own? Osama bin Laden has made his choice. Who says your choice is right and his is not? Can you convince him that he should stop trusting his own judgment and follow your morals?

Second, if you have this much discernment to know instinctively which part of the religion is good and which part is not, then why you need the religion as the guide?

I use a map when I am lost to find my way. If the map is only fifty percent of the times right and the other fifty percent of the times sends me to a wrong direction, what is the use of that map? By consulting that map I never know whether I am going to be guided or misguided. To know which part of the map is right and with part is misleading I have the full knowledge of the place. In that case I know more than the person who drew the map. Then why in the hell I need to consult such map? Why would I recommend it to anyone?

If you ask a direction from someone and he points his right and left hand to two opposing directions, would you trust that person as a reliable guide? Won't you say he is nuts? 

Furthermore, the Quran claims to be absolute truth. It does not allow questioning or disagreeing. Once I accept that book as a book of guidance how can I disagree with anything it says?

Another example: You go to a doctor and he gives you some medicines. Some of them are good for you and cure you and some of them kill you. How do you know which medicine is the good one and which one is the bad one? To know that you must be a better doctor than the one you visited. In that case why you need to visit a less competent doctor than yourself?

Once you agree in principle that even one of the teachings of a religion that claims to be from God and the absolute truth is not right, the entire religion is to be discarded and flushed in the toilet. It becomes entirely worthless.

In Islam there are hundreds of things that are wrong. Almost everything is wrong. Hardly you can you find anything good in it. But if you find one or a few good teachings, are they worth the risk? Can you show me any ideology, including Nazism that has nothing good in it? Nazis gave a lot of importance to sport and physical fitness. Can you say that because of that Nazism is not that bad and it too has some merits?