Sanderson Jones, co-founder of the Sunday Assembly, wants it to be more diverse. I know this because he sent me an email a few months ago to invite me to speak at the one-year anniversary of his “atheist church” in which he said, “We are going to do [an Assembly session] on new year’s resolutions, and one of our new year’s resolutions is to try to become more diverse in all ways.”

I accepted the invite, but something about Sanderson’s email bothered me and I wrote back saying, “I admire your desire to be more diverse in your speaker line-up . . . But it does leave the question of whether I’m being invited to speak because I meet your need for diversity or because I’m genuinely someone who you think makes for an interesting potential speaker.”

Sanderson wrote back and said: “I would love you to speak at The Sunday Assembly, because you are great full stop.”

What else could he write? However, Sanderson went on to say, “Next year we also want to make a real commitment to increasing the diversity of our congregation, because unless you make that something you actively pursue, it is forgotten.”

It was this that made me completely comfortable with accepting Sanderson’s invitation, despite the clumsiness of his initial email to me. Sanderson is right: diversity is important and it’s important to be active in promoting it if you want your organisation or community to be genuinely diverse.

It’s not necessarily obvious why “diversity” should be something that should concern those who run the Sunday Assembly. A couple of years ago, I wrote a piece for the Guardian’s Comment is Free in which I suggested that the atheist movement could do more to welcome people from black and Asian backgrounds. Having worded the piece very carefully I, perhaps naively, didn’t expect it to generate much controversy, and was surprised by the hostility of the responses. Numerous comments suggested that it was not the responsibility of atheist groups to seek a more diverse audience, with one fairly typical respondent arguing that “the onus is on minorities” to get involved in such events.

I’m a physics teacher, not a sociologist, but even with my limited academic knowledge of these matters I can confidently state that we live in a patriarchy and, in the West at least, we live in a world where rich white men occupy most positions of power. The concerns of rich white men are given priority in society, and the values and beliefs of rich white men dominate our public discourse. In short, we live in a world where rich white men matter more than the rest of us. This is something we ought to change; it is immoral to maintain a state of affairs that unfairly privileges one group of people over the rest.

There really shouldn’t be any need to explain to anyone that fighting racism, sexism and classism will ultimately make the world a better place, but it seems that any mention of “diversity” can get some people’s backs up. I’m well aware of how divisive talking about diversity can be – there’s an irony in the fact that in focusing on diversity we can over-emphasise our differences and, instead of creating greater understanding and empathy, end up further alienating ourselves from each other. But embracing diversity isn’t just about avoiding the negative consequences of not doing so. It can, and should, be a positive thing. Encountering diversity challenges us to examine our prejudices, to see not just the world but ourselves in a different light, and gives us the opportunity to discover aspects of ourselves that we may not know exist. It can help us realise the possibility of being someone new, someone different, someone better. So, since the Sunday Assembly states that one of its aims is to help people to “live better”, promoting diversity should indeed be close to the top of its agenda.

The existence of the Sunday Assembly gives the lie to the idea that there is no such thing as an “atheist community”. There are other atheist communities, both online and in the real world, and it is in the interest of those communities to ensure that they are diverse in their membership, and their leadership, or they risk perpetuating the status quo.

Atheism is an incredibly liberating worldview, one with the potential to transform the world for the better, but it will fail to do so unless atheist communities welcome those who are marginalised elsewhere in society. If, as atheists, we truly want to live in a more just world, a world where there is less inequality, we must, like Sanderson Jones, actively pursue diversity.