Atheism evangelism followup

I posted a comment on hahathor's post about evangelical atheists, and since I never followed up on my post about it here, I figured I'd repost part of the comment here.

The thing that spurred me into asking [whether atheist evangelism was any better than religious evangelism] was this: I saw a documentary about evangelists where someone explained that, if you truly believe that someone you love will go to Hell because they are not a Christian, then shouldn't you do everything you can to prevent that loved one from going to Hell? It does make logical sense, if you accept the assumptions of Sin and Hell. And it made me think, hypothetically speaking, if I truly believe that someone I love is doing damage to themselves because of their religion, then shouldn't I do everything I can to convince them otherwise? For instance, suppose I knew a Christian Scientist who was suffering from a treatable illness, but who refused medical treatment in favor of prayer. If I cared about this person, shouldn't I try to convince them that medical treatment is far more likely to be effective than just prayer? Maybe this doesn't count as evangelism, since I'm not trying to convert them completely to atheism, just away from a particularly egregious corollary of their religion. But it falls into the category of "disabusing others of their beliefs". This is an extreme example, but I think this is the kind of motivation that spurs people to talk someone out of a religious belief: the stereotype is that religious people do some irrational things based on their religious belief that can sometimes be harmful to themselves or others, and if you think that this might happen, then in theory it's socially responsible to try to change their mind. But, yeah, in practice it's usually just rude.

To be clear, I personally think evangelism of any sort is usually a bad idea, not just because it's rude, but also because in general it's dangerous to assume that you know better than someone else what's good for them. But I think the motivations of atheist evangelists can be as virtuously-intended as religious evangelists who want to save your soul from eternal damnation.