Atheism
is a religion within itself. A religion with the core tenet of 'God does not exist'.
Like any religion, Atheists do their fair share of proselytizing and preaching their philosophy to all and sundry.
They are just as passionate about their 'no God policy' as believers are
about God.
Atheists all want to 'wake up deluded people' who still believe in an illogical, irrational deity, because they see it as being the downfall of society and also, others beliefs in a God are having a negative/detrimental effect on their personal lives and they wish to change that.
They cannot change another's beliefs, so they become officially 'Atheist' to cement their resolve.
Atheists shouldn't worry about what other people believe in if they don't, but like I said, Atheists are just as mad about proselytizing as Muslims and Christians are - if not moreso!
They want to see a world ruled by science and logic, where God has no part of that.
Little do they know, they actually have no say in it.