Atheists are not irredeemable, and atheism is not some special, horrific unpardonable sin. I would imagine that a disobedient Christian would be in worse standing than an atheist.

I think the key lies in whom Jesus criticized.

It was not the Roman pagans. It was not the prostitutes. It was not the thieves. He was kind to the man on the street who was snared by error and sin and came to heal, edify, and set people free.

Jesus targeted the money changers in the temple and the self-righteous Pharisees who led the people astray. That is whom he condemned.

In the last days, these evils will manifest themselves as the mark of the beast and the harlot.

Money changers in the temple = mark of the beast (without which you cannot buy or sell) defiling the human body (the temple)

The Pharisees who brought Jesus before Pontius Pilate to be crucified = the harlot church, false prophet uniting with the beast system to persecute Christ's followers.

We do not fight against flesh and blood. Our enemies are spiritual powers and principalities. Stop picking on the poor guy standing next to you. Despite his lifestyle or beliefs, he is not your enemy.