Common misconception.
Atheists are people, and therefore agents. But atheism is not a motivation even for us.
Anti-theism can be a motivation. Reaction to presumption of theism from the social environment may be a motivation. Even existential angst hypothetically related to atheism might conceivably be a motivation.
But Atheism proper is not a motivation.
.....and neither is 'theism proper.' The problem here is the fallacy of composition, and though both sides commit it, atheists seem to be more wedded to it. In fact, both sides commit the same brand.
Theists, when some atheistic group does something VERY 'religious like killing people because they are religious, or trying to pass laws prohibiting religious rights and freedoms, attack ALL atheists, not acknowledging that while some atheistic groups may be anti-theist, not ALL are.
Atheistic groups which may be guilty of attempting to limit religious rights, when getting reamed for doing something horrific, claim that since the whole class 'atheism' means only 'non belief in deity,' then ALL atheists have ONLY that property. That is, if 'atheism' is innocent of wrong doing (since it's only property is non-belief) then all atheists are equally innocent of pushing their non-beliefs upon others.
As for me, if it walks like a duck, etc., it's a duck. An atheistic group that does exactly the sort of thing that they claim only religions do (that is, attempt to force their opinions regarding deity upon others by law or means more coercive than talking) that group, to me, is just as 'religious' as any hide bound Puritan 'put 'em in the stocks for being late to meeting" group ever found.
Quack.