In our current world, atheism isn't considered heresy in most places. In the US, for example, we have freedom of religion, which includes the freedom to not belong to any religion. But in Vorin society, basically everyone is a believer, and they are much more strict about it staying that way, which is why Jasnah is considered a heretic. I agree with your second point though, but I don't remember the context of her saying that.