A very nifty book

I just finished reading Morality Without God by Walter Sinnott-Armstrong (http://www.amazon.com/Morality-Without-God-Philosophy-Action/dp/0195337638). Its a very short, simple read, and congenial read. I would certainly recommend it. In this book he tries to refute these 5 statements:

1)That athiests cannot be moral, or that they are inherently immoral

2)Society will sink into chaos if it is secular
3)w/o fear of divine retribution we have no reason to be moral

4)that objective moral laws do not require God's existence

5)w/o religion we can't know what is right or wrong.

Claims 1,2,3,5 are rather juvenile and he has no problem refuting them successfully. However claim 4 is  in a little more contention. Essentially it is the argument from morality for God's existence;

1. If there are objective moral values then God exists (moral values are dependent upon God) 

To refute this he critiques divine-command theory and explains a "harm-based morality." The critiques of divine command theory mostly has to do with the classic Euthyphro dilemma and other difficulties. I did find the Harm-based morality rather attractive, because of its simplicity. It goes as follows:

• 
Action x is wrong because it harms the victim for no adequate reason. 

 To see if this is an adequate take on objective values one would have to explain several things; what are harms, what is in adequate reason, and why should one be moral? 
Harms include: death, pain and disability 
An adequate reason is a reason which prevents further harm.

Why should one be moral? Well this is a self-refuting question if it is asking for a moral reason to be moral. However if we are looking for another reason, what could/would those reasons be? I am not quite sure.