All religions are caught in a bind. A bind none can escape and dooms them whichever option they chose. The bind is at the core of all practicing religions and cannot be ignored. The bind is over the unignorable question of what to do about non-believers. How should churches view those who do not agree with them? It is considered cruel to threaten them with Hell yet if they do not they are implying their rules do not matter. There is no third option that is both compassionate while maintaining the integrity of the church. Either way, religion loses.
Non-believers were traditionally persecuted and it was assumed they were all going to Hell. Apparently punishment in the next life was not enough, so people who did not match the ruler’s religion were persecuted and suppressed. Christians persecuted Muslims, Muslims persecuted Christians and everyone persecuted the Jews. The history of the Middle Ages until the Age of Enlightenment is essentially a history of religious wars. It is for this reason that most countries had only one religion. The Inquisition is the most famous example of the suppression of non-believers with public burnings, but there are countless others.
From the 19th century or so onwards, the persecution eased up and moved to less violent forms of repression. Laws were still based on the dominant religions teachings and minority religions often had fewer rights. To be a non-believer justified poor treatment, harassment and second class citizenship. Even into the middle of the 20th century, Catholics were still told that Protestants were going to Hell for not belonging to the “One True Church”. This is still believed by many fundamentalists of all religions and persecution is still rife in many parts of the world.
At this point many religious people may object, saying I am relying on the common Atheist tactic of focusing of the extremes. They argue that while the Church in the past could be brutal and repressive, the modern Church kind and tolerant, willing to embrace all walks of life. This modern religion claims love as its central doctrine. It holds little against Muslims or Jews anymore and instead embraces diversity. Many priests now say that God loves all people and even people from other religions can go to Heaven. Pope Francis even went as far as to say that Atheists can go to Heaven if they are good people.
However, this causes a serious problem for religion. You see the whole point of organised religion is that interprets holy books and provides rules for people that supposedly came from God. If being a member of that religion is not important, than you are implying that its rules are not important. If someone who isn’t Catholic can still go to Heaven and enjoy all the same benefits in the afterlife, then what is the point of the Catholic Church? Surely you can then disregard everything the priests say and ignore all the rules without being any worse off. If being a good person is the only requirement for entry to Heaven, then religion is obsolete.
Of course, a religious person would contest this and argue that it is necessary to obey at least some of the rules. They would believe their church plays some necessary role that requires some obedience. However, to do this we must then assume that non-Catholics (or whichever religion) cannot enter Heaven or at least not on equal terms. For organised religion to have any validity there must be some degree of exclusion.
Of course this is grossly unfair (as most religious people would agree). Religion is like nationality, it is almost never chosen but rather inherited from your parents and based on where you live. People are Catholic or Muslim or Hindu, not because they have examined all the religions of the world and found one that best suits their worldview, but because they were born in Colombia or Libya or India. Most people know next to nothing about other religions and thus it would be exceedingly cruel to punish them for something they never encountered. To say everyone who is not a member of your religion will go to Hell, is equivalent to condemning 85% of the world to eternal suffering just due to where they happened to be born.
So religion is stuck between a rock and a hard place. It would be horrendously cruel and intolerant to condemn all those of different religions to Hell due to the luck of birth, yet to fail to do so undermines the sacredness of their rules and teachings. Religion must be exclusive or meaningless. Either intolerant or irrelevant. Religious readers, take your pick.