Why do athiests have morals?

This topic came up in a craigslist forum on religion.

It reminds me of a discussion i had in college with one of my really
good friends who is an athiest. I constantly asked him why he didn't
just kill people and do drugs.

if you lack a God based worldview.
if everything around us really is an accident.
if our brain synapsis are just a piece of evolution
and if there is no objective truth.

then there is certainly no reason for morals.
if someone gets in your way, they might as well die, they're just
dust. they're no better than an ant. or even a rock for that matter.

if i lacked a christian worldview, i would lie cheat and steal till my
hearts content. the worlds consequences wouldn't matter anyhow.
drugs would be probably be the name of the day.

without a christian worldview, there genuinely is no good reason to be
moral. to have morals.

so why do they?

are you an athiest? why are you moral? help me understand.