Why is that? If the primary lesson of the bible is tolerance and acceptance of those different from yourself. Those who founded our societies who were religious people apparently thought this tolerance of others was important enough that it needed to be put into the constitutions of all of those nations.
They did this based on real-world governing utility. We don't know that they did it based on what the bible said. They were religious men, but with the type of nation they were trying to build after living in what they perceived as tyranny in England it's kind of obvious that they'd go with religious tolerance.
Are you saying that the bible doesn't say that non-believers go to hell? The book as a whole isn't too keen on understanding that some people won't agree. It calls for faith in itself. The basis of the religion is that we are fallen as a species and the only way to be saved is through god. Jesus died on the cross to pay for our sins, and without that happening we would have been damned for eternity. Our souls are saved through faith in the Christian god, according to the bible. It's pretty clear, in my opinion. I'm interested in your take though. I'm all for hearing dissenting opinions.