And besides, what's the point? If atheism is true, why does it matter what people believe, as long as they are happy with it?
It's actually a wicked conundrum! If people are happy in believing a falsehood, it's a real question as to whether that falsehood should be confronted! The only way it's at all justifiable is if you think that you need to shatter the falsehood in order to give a better truth. That's awfully paternalistic, and people have to struggle with the temptation of thinking that "they know what's best for you". They might, but they might not.
Now, if someone claims to be truth-seeking, then what can you do? You just have to trust that they're being honest, and would rather know the truth (and unhappy) than happy and wrong.
But, there's also a question of the greater good. If one holds the axiom that having knowledgeable citizenry will help make the world 'better' more quickly, then you're going to want people to know true things, so that false things are not propagated.
And, lastly, there is the problem where people's false beliefs will cause a problem, because the problem is derived from their errors. If we see a problem happening, and a source of that problem is due to a false belief, then the belief needs to be confronted.
Unfortunately, sometimes we're dealing with a house of cards. Attacking the part that's a
problem will upset the other parts that're not that bad. Some atheists are happy to help reconstruct the house-of-cards, in order to mitigate the 'unhappiness' they cause. Others (who're maybe more prone to self-justifying, and more prone to valuing truth over falsehood) might not bother with helping reset the house-of-cards, and are happy to knock over the whole thing.
Unfortunately, another conundrum also presents itself. An incredible number of faithful self-report that they would become 'less good' if they lost their faith. What do you do then? If you see their faith is causing some harm, but know that they might 'become worse' if you attack their faith, then it's a real balancing act! Do you trust that they're more innately decent than they think they are? Do you believe their self-report?