How would you answer an eastern European atheist who grew up in communist state atheism, and was taught that religion is a way for authorities to make people compliant and honest, and as a way to control people for the benefit of society as a whole?

My first thought was: We should agree with him. Religion is powerful, because we are spiritual by nature, and therefore it can be tempting to use it as a weapon.  It is the conclusion the atheist draws about God, however, that needs to be questioned, not his observation about how religion is used to drug the people into submission.

We are spiritual by nature because we live in a spiritual world.  We reject Karl Marx’s “soulless conditions.” How would Marx know whether there is a soul or not?  (I refer to the introduction to his A Contribution to the Critique of Hegel's Philosophy of Right.) We have experience of this -- perhaps he did not.

The fact that atheist governments have used religion to control people in no way invalidates faith.  (Although it’s probably truer, at least in the past century, that atheist governments have attempted to suppress religion, since it may interfere with political allegiance.)  At any rate, if religion truly benefits society, then perhaps atheists ought to be more positively oriented towards it!