You must have engaged with a theist who claims that atheists have no basis for morality, and with their claim of morality being subjective then atheists cannot maintain that rape or murder is wrong, so are free to rape and plunder without consequence? This is a prime example of how religion removes any notion of rationality or logic.
I’m an atheist, and a humanist who’s a supporter of secularism, antidisestablishmentarianism, and quite anti-theistic in my views, as I strongly think that religion is the root of the majority of the history of the world’s evil and corruption. Many religious groups are misogynistic, racist, oppressive, judgemental and corrupt. Just look at the Catholic Church as a prime example of corruption. Is there a larger criminal organisation?
Despite being outspoken about anti- theism I’m still of the mindset that people are allowed a choice, and if they choose a faith, then it’s their right as a human being to practise it. But does them following a religion, and its rules make their moral decisions more ethical than an atheist? Of course it doesn’t. Bad people do bad things, and good people do good things and labelling yourself as a Muslim, an atheist or a Christian doesn’t mean you’re incapable of being bad or good. I’m in a monogamous marriage, I have a full time job where I pay my taxes, I’ve no criminal record as I’ve never been arrested and other than curse at someone I’ve never caused another human being any harm. I support a number of charities, and I’m a vegetarian as an ethical decision as I believe all sentient life has a purpose. Yet in the eyes of certain people who troll social media, I have no basis for morality so anything goes.
From a young age the majority of people are taught by their parents and then school teachers what’s acceptable and what’s unacceptable so you’re prepared to live in a society that has expectations. Although consequences for actions aren’t initially understand, a child becomes aware as they mature and get a better understanding of the world around them. The majority of people develop a conscience, which is a moral sense of right or wrong, and if you hurt someone you often get a feeling of guilt or remorse, and once you engage empathy and you walk in that person’s shoes, you realise that you wouldn’t want to be in their position. The older a person gets, the more they should understand that human rights are essential to successfully thrive in a society, and any infringement on those rights ie: rape, murder, theft is unacceptable. No one needs an ethical guideline from religious scripture to inform them what’s right or wrong.
If a 2000 year old book suggests that two men laying together is a sin, what makes that objectively moral? It’s allegedly the words of God, but what makes the decisions by the God the foundations of morality? How are two people of the same sex, in the privacy of their own home, causing no one any harm as they are consensual adults a sin? Because a God that the believers can’t even prove exists says so?
For something to be objective then it can’t be influenced by feeling or opinions, it has to be deeply rooted in facts. Christians cannot prove without a shadow of a doubt that YHWH exists, Muslims cannot prove without a shadow of a doubt that Allah exists, so it’s down to personal belief, and that’s subjective, not objective. So all we have is subjective morality, and it’s choices we make that can affect people in a positive or negative way.