The concept of "no good without religion" has a pretty decent intro with both sides at https://en.wikipedia.org/wiki/Secular_morality#Morality_requ...
Personally utilitarianism, often held as the secular morality, threatens to go down some really dark paths and has done so. You could easily see how things like eugenics (widely practised in the West until the Nazis put it beyond the pale) became popular, and it was the Catholic church who led the fight against it.
And indeed, as I said my way of thinking gives me huge library that suggest me what to do and what is good and what is bad.
Most importantly I think that human beings ( and animals in that matter ) have really big spectrum of emotions that we carry over thousands of years that are not here today, because we need to fight them.
Fear can save your life sometimes ;
Anger ( adrenalin ) can make you a better fighter in time of trouble ;
Jealousy sometimes give motivation of doing good deeds ;
etc.
If the results of those emotional decisions are not regulated by law and only by moral ( of your cultural ancestors, family, education, etc. ) then I really think it's up to me to decide, otherwise we will all be copies of the moral we inherited and there will be no change at all
1 : http://www.law.harvard.edu/faculty/shavell/pdf/4_Amer_Law_Ec...
Let me respond to your counter question.
I'm considering myself as an atheist. I graduated law and (but) I'm currently working in IT.
What I found about myself and my own beliefs ( good vs. bad ) is basically a consequence of thousands of years of human civilization absorbed and morally embeded in human beings and in logically written laws.
So basically what I believe doing is good or what I believe doing is bad is defined purely based on logical concepts, incorporated mostly in our legal systems. Yes there are different legal systems, there are different cultural standards, but if you take a look at it, I bet :
1. Every legal system punishes killing, stealing, frauds, etc.
2. Every legal system has an exclusion of the first rule : self-defense, non-voluntary ( accidental ) steal, etc.
3. Every legal system also regulate the civil rights of people agains other people. ( Continental Law states that for a divorce there is a blame that might lie in one of the partners, based on this the other claims compensation - imagine cheating ).
So yes. You can find multiple examples for the most of the actions and you will see that they are mostly regulated.
e.g.
1) You found a passport on the street - By law you are obliged to return it to police ( good deed )
2) You drink a beer on the street - Based on the law you can decide if this is well received or not ( In Berlin it's pretty much everywhere )
etc.
For all other actions, that have no consequence in society and which are not regulated. I choose based on my own opinion and mood.
e.g.
1) Should I give a penny to that homeless person? Well If I feel in the mood, I would, If I don't I probably won't do it today.
2) Should I talk back to a rude person? If I feel really offended, I will most certainly do, usually I don't give a F.