Why do Atheists insist on telling others that God isn't real?

It's ok if they don't believe in God, but why do they feel the need to enforce their own opinions and beliefs onto other people? Especially to people of other religions like Christianity, Catholicism, Jewism, etc.

I remember an Atheist who literally told other Christians that there's no evidence that God is real, basically telling them what to believe, why are some Atheists like this?

Why do Atheists insist on telling others that God isn't real?
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