A little over a century ago, our first prime minister told our first parliament that “the doctrine of the equality of man was never intended to apply to the equality of the Englishman and the Chinaman”. Barton had the abstract principle right, but he couldn’t see non-Europeans as the sort of people to whom it could apply. He could not see their inner lives, their concerns, passions and beliefs, as being as morally significant as his own.

In his recent book, The Better Angels of Our Nature, Stephen Pinker points out that for all our talk of moral decline, we are actually living in the least violent, least cruel and most peaceful era in human history.

Much of this progress, I’d suggest, is due not to better moral reasoning or principles, but to our improving moral vision.

We have come a long way since that first parliament, and we’re learning – gradually, fitfully, and painfully – to see what Barton could not see, to view others as no less worthy of our regard on the basis of irrelevant differences such as race, religion, or sexuality.

But what happens when the competing demands of religious and sexual identities collide in the public sphere?

The Gillard government has announced it will preserve existing exemptions in anti-discrimination legislation, allowing religious organisations to refuse to employ LGBT individuals – and indeed anyone else whose very presence might cause “injury to the religious sensitivities of adherents of that religion”. The Australian Christian Lobby has hailed this as a win for “religious freedom”.

This is disingenuous at best. The issue really has nothing to do with the free exercise of one’s religion and everything to do with denying the moral depth of gay and lesbian lives.

To be clear, we are not simply talking about issues of job performance. It’s hard to see how being gay would be an impediment to doing many, if any, of the diverse jobs available in the various faith-based charities, schools, hospitals and universities around Australia.

Rather, groups such as ACL are defending the “right” to refuse to hire someone, not because their actions might be contrary to the mission or ethos of a religious employer, but because who they are might offend against someone’s “religious sensitivities”. It is a rejection of who the employee is, not what they do.

This fact is sometimes obscured by calling homosexuality a “lifestyle” – a deliberately shallow, superficial word designed to deny the profundity of someone’s core relationships. It implies that homosexuality is some sort of inessential add-on rather than a defining feature of the person. My relationship is a central, non-negotiable part of who I am; your relationship is just some stylistic choice, like installing marble benchtops or wearing Crocs.

Sometimes, instead, discrimination is justified by claiming that what’s hated is the sin, not the sinner. This may be a sincerely held view, but it too ignores just how deeply integral romantic and sexual love is to our practical identities. It denies the same depth to same-sex and heterosexual relationships, and so implicitly refuses to acknowledge the significance of what it claims to be offended by.

The question here isn’t whether (some) religious believers are right or wrong to be offended by homosexuality in this way. Nor is it whether we should respect the deep religious convictions of believers.

Rather, it’s whether society is obliged to respect this sort of offence enough to override other moral considerations. And this takes us to the clash between private faith and public moral reasons.

Religious faith, however it finds expression, is an essentially inward, private state of profound certainty. It may involve reasons, but these are not the sort of reasons that can be shared with non-believers. I doubt anyone has ever been moved from atheism into genuine religious faith (as opposed to mere lip service) by force of rational argument alone. Trying to argue someone into religious belief is like trying to make someone fall in love with you by telling them all the reasons why they should: it won’t work, and even if it did, it wouldn’t be because of your arguments themselves but because of something else.

For some believers, then, there may be an unshakable inner certainty that homosexuality is immoral. It would be wrong for those of us who disagree to simply trivialise that view, as it may be linked to fundamental beliefs that are central to the believer’s conception of him or herself and what a good life comprises. I’ve heard Christians say how torn they are between their love for gay friends and family and their belief in the authority of scripture. I don’t doubt their sincerity, nor the difficulty it presents them.

But when it comes to matters of public ethics, beliefs that are grounded in religious faith simply don’t cut it on their own. Believers and non-believers have to share a society, and that means our moral discourse has to be based on premises it’s at least possible for us to agree upon. “I find working with gay people offensive because God says homosexuality is wrong” is simply not such a premise.

It may be an important fact about the lives of some believers, but it doesn’t justify employment discrimination. Surely we’ve come at least far enough to see that.