The complete slogan reads: "There's probably no God. Now stop worrying and enjoy your life."
No religion has ever set its followers free from the oppressions of the organized hierarchy of that religion (with the possible exception of the historical Jesus himself). Religion teaches unquestioning obedience. Religion is slavery. I oppose such slavery as earnestly and staunchly as my ancestors opposed the slave ships and the slave policies of the Confederacy.
I am not anti god (for one can hardly oppose something which does not exist). I simply wish to set people free from all forms of oppression and exploitation.
The ruling elite loves a population trained from birth to confuse beliefs with the real world. It is much easier to rule a population, pillage them with taxes, or send them off to fight a war, if the ruler is not required to prove the reality of his or her propositions and statements. This is why, since the dawn of civilizations, governments encourage their people to be ruled by beliefs and not by reason. It takes chains of steel to enslave a rational human, but all the rest may be enslaved by a belief.
Throughout history, a wide variety of religions worshiping Molech, Baal, Odin, Jupiter, Zeus, Ahura Mazda, Jehovah, Allah, Quetzalcoatl, Coatlicue, Vishna, and others far too numerous to elucidate here have come and gone.
The followers of each of these religions believed that theirs was the true faith and contained within it the correct answers to life's great questions. All too often followers of a faith were ever eager to cut the throats of those who disagreed with them.
But on many of the most basic aspects, mankind's multitude of religious thoughts contradict each other. On what would seem to be the most basic truth of all, just how many gods there are, the various religions throughout the world are in complete disagreement. It therefore follows that most of the world's religions, if indeed not all of them, do not have the correct answer to the basic question of how many gods there are. They cannot. For one to be correct means the others are incorrect. Yet the followers of each religion believe they are correct, even though this is impossible.
Ergo, belief that one is correct is not in and of itself proof that one actually is correct.
If one posits the existence of a god or gods able to communicate their presence to human minds, then as an inevitable result of the existence of that god or gods, it would be expected that all humans, or at least the priests who claim communications with the god(s), would have a unanimity of opinion as to how many gods there are.
Likewise, if one posits the existence of a god or gods able to communicate their existence to human minds, then as an inevitable result of the existence of that god or gods, able to communicate to human minds, all theologies would be in accord, and there would be no need for missionaries, let alone inquisitions and holy crusades.
But there is a diversity of opinions as to how many gods there are. And there are missionaries, crusades, the inquisition, and the burning of a million heretics.
The world is not as it would be if there was a god or gods which could communicate their existence to the minds of humankind. None of the conditions which must inevitably follow the existence of a god or gods able to communicate their existence to the minds of humankind can be found anywhere on Earth.
Quod Erat Demonstrandum, no such gods exist.