How to easily defeat any argument for God

[Simon Moon]

That was Simon Moon. I happen to disagree

So there is no objective morality, every atheist has his own opinion.

Even if every atheist has a subjective opinion of morality, that does not make their subjective opinion, moral. If it interferes with other sentient beings well being, it is immoral.

There is a difference between situational ethics/morality, and subjective morality. Most theists are unable to understand the difference.

It is impossible to be nice to atheists that killed 100 million people

First, I'll go for the low hanging fruit. Hitler was not an atheist.

Second, even if Stalin, Mao, Pol Pot were atheists, their motivation for their mass murderous regimes was not disbelief in gods. Their motivation was being totalitarian dictators.

What they actually did, was replace the bad dogma of an infallible god, with the bad dogma of an infallible State. Bad dogma leads to murderous regimes, not disbelief in deities.

If atheism makes for such murderous countries, how do explain; Sweden (80% atheist), Denmark (70% atheist), Norway (70%), Japan, France, Finland, all over 50% atheist populations. Where are the mass murdering Swedish regimes?
What they actually did, was replace the bad dogma and doctrine of an infallible god, with the bad dogma and doctrine of an infallible "State". Bad dogma is what creates totalitarian murderous dictators, not lack of belief in deities.