The misconception stems from the notion that morality requires a law giver.
Let me jump in.

My first post. Thank you for the opportunity

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That is very good but Western society (and therefore the whole world) has permeated with Christian ideas. How many of these have rubbed off on you and formed your system of morality? Your parents were no doubt a contributor to how you see morality - treat others as you yourself would like to be treated. Your parents took this from their parents and they from theirs.
Atheists don’t see moral concerns as having anything to do with pleasing or displeasing deities.
That is only part of it. As explained already, and for some reason many atheists fail to grasp it this is not the only issue. Other reasons can be feeling gratefulness to God or
aspiring to follow in Christ’s footsteps - where He is an example of how to live one’s life - less selfishly, more lovingly, with less violence, less prejudice, etc. Christians believe that if someone as great as God created them and other people (including non-Christians and atheists) then there is an additional reason to love (respect) those people (everyone else in this world). This all in addition to any instinctive feelings for children or altruistic feelings we all (atheist and not) may have. The one does not exclude the other.
We think that moral concerns are concerns for the well-being of others.
Not speaking about you personally but perhaps that only works out well when we are comfortably well off? In times of war, for example, or famine, would the same still hold?
Would you give your last meal to someone else?
We love our children as much as you love yours.
Suppose your son was in competition with your neighbour’s son for something very important - an opportunity of a lifetime. Suppose you could get rid off your neighbour’s son without anyone noticing and the authorities prosecuting you. In such a case, would you not do it? Would your son not matter more to you than a neighbour or even a stranger’s son?
Perhaps you knew your son was better and he would contribute more to society in the long term - perhaps doing away with that competitor in a humane and painless way would be the way to go? A Christian may (and not necessarily would) have thought along these lines - that other guy is also a child of God, if I kill him besides the fact that he and his parents will suffer - I will have committed a grave sin in front of God. Also despite the sin, this God, he made me and him, and now I do this in return? And so on - different people may think differently but along similar lines.
Like you, we want to leave the world a better place for having been in it for a brief time.
So did Mao, Pol pot, Hitler, Stalin etc. They all meant well. They wanted to build strong egalitarian societies and each one thought they were doing the right thing but because they had no ‘old fashioned’ or ‘sentimental’ ideas such as Christianity (even the basics thereof) they could do what they thought was right. Marx believed that genocide was unavoidable as inferior races who were not able to accept the Communist utopia had to go and be exterminated. His followers, Hitler himself read and admired Marx were following on this ideology. Many great thinkers such as Bernard Shaw himself wanted to gas the idle and unproductive in the 30s and when asked about the human suffering in post-revolutionary Russia a famous leftists said that “you can’t make an omelette without breaking a few eggs”. Even if we looked at the functionaries of these regimes, the guys who gasses, bayoneted or shot human beings - they did what they did because they often believed it to be right. The notion of God was forbidden, and it was thrown out by their masters and these people had no concept to cling on. Where these people all inhuman without consciences? No. Most of them had wives, children and families and they were caring parents.
Also, your comments about what an atheist can do to an old person ought to be compared to what a Catholic bishop can do to effect the lives of victims of sexual abuse. All humans are capable of evil.
This is very true. Everyone is capable of doing evil. Catholics did evil to - and still do. The clergy still perpetrate evil but that evil is not per direction of the teaching of Christ. Just because someone wears a robe does not make them good. We’re not arguing that.
Without God, or belief in God, and some fixed knowledge that there is something greater than the hype, lies and cynicism of politics, peoples’ minds can be filled so much easier with lies, especially in stressful situations - such as war, revolution, famine, natural disaster when society breaks down and life becomes survival of the fittest.
I recently watched a Soviet era film from 1985 - in it the SS are exterminating Belorussian
civilians. Upon capture by partisans the partisan leader asks the leading SS fanatic why he wanted to kill the children and spare the adults - his reply was that ‘it’ (problem of other races taking up space from Germany) starts with the children. Many Germans, Japanese, Cambodians, and others did this in real life in WW2. Despite instinctive feelings towards their own (genetics, upbringing, neurotransmitter levels in their brains) they could dehumanise the Jews, Slavs and Chinese and perform on them
incredible cruelty in the name of a greater good. Now that greater good wasn’t just to make an atheist state (atheism can’t be blamed for that) but what we can blame atheism for is that without belief in God these people would find it easier (or even possible) to do what they did. If these people were strong Christians, they would have rejected the rhetoric of their leaders and never signed on to do what they did.
Thanks for the opportunity

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Best, T.