It all comes down to where you think ethics come from...
I've studied this to a large degree, in conclusion it stems from a desire/need to preserve ones self and the human species. The things that do less harm and brings more happiness are considered the most ethical and moral
No need for religion to tell people what is and isn't moral. in fact, religion makes people do morally questionable acts, such as killing people for various reasons... I recently found out that in Islam, IF that dude who is burning the Qur'ans was in a muslim country, the rule in islam is for him to be KILLED, as stated by the Qur'an/Prophet, same goes for people who talk bad about the prophet and God - death
so no, I don't think atheists are immoral, quite the opposite in fact in my opinion
