Do atheists lack a conscience since they seem to be lacking a soul?

No, they definitely have a conscience. I say this because they try so much to put Christians' beliefs down, reviling us. You see GOD is constantly speaking to their souls; asking them to repent of their sins and turn to HIS Son, Jesus Christ for their redemption. By doing this, their conscience is being tormented just for being atheists; which is why they seem so angry all the time.