If by “one man’s opinion is equal to another’s” you mean that no one will judge either one in the afterlife, you’re right. But if you mean that their opinions will have equally advantageous results for humanity, then no, you’re wrong. But you don’t need a God to tell you the difference between a happy, thriving culture and a pile of murdered bodies. Do you? I don’t.
Notwithstanding, His Truth [Logos] alone is the difference between "a happy, thriving culture" and "a pile of murdered bodies."
Cultures — societies — that produce piles of murdered bodies historically have all been atheist ones.
Do you think our present-day American society is a "happy, thriving" one?