It would seem that the main problem with anyone who chooses not to believe in any scripture, is the fact that following any kind of rules, other than those that said person has set for themselves, is highly disagreeable to them. Man is a funny creature. We can look at the order of the universe, our planet, the seasons, birth, anything really and see the order in it. Literally seeing the order of creation right before our eyes and then say, "I need proof." To each his own I say.
"Die before you die."-Prophet Muhammad (Pbuh)