Ask them, can a christian do evil things? Can a believer in god do bad? Maybe sin? If with god people can still do bad, what makes them think that without him no one can do good?
See Bill Gates. Atheist. Donated 60 billion to fund health programs in third world countries among many other things. Have them explain that.
At the end of the day even the New Testament recognizes what really matters. It is not words but actions (Luke 10:36-37). What you do is the best argument you can present to them.
Remember that “If people are good only because they fear punishment, and hope for reward, then we are a sorry lot indeed”.
We do good for goodness sake. Doing right it is its own reward. Secular morality at best. For a longer discussion about morality in absence of a deity check the topics in point 5 on the FAQ.
The level of unplanned pregnancies among young people is a major global issue, campaigners say, and the rise in unprotected sex in several counties has sparked concern about the quality of sex education available to youngsters.
Thank you so much abstinence only evangelicals and anti-condom Catholics. You have achieved another disservice to humanity.