The simple answer is that, if one is convinced that religions are not real (not even necessarily an atheist, a deist can believe this as well) seeing their love

The simple answer is that, if one is convinced that religions are not real (not even necessarily an atheist, a deist can believe this as well) seeing their loved ones "wasting" (again, according to them) their lives on things that do not exist kicks in an instinct to "protect" these people. This is the simplest explanation of why people try to convert others to atheism. I'm not making a judgement call, I'm just explaining why people do that. As an atheist (well, I identify as an ignostic [1] which I view it so be a subcategory of atheism) I don't go convince people to be atheist. This is partially because all my close friends are already irreligious; and partially because religion is inflammatory so the cost/benefit trade-off isn't in my favor. However, if I had a very close friend, say my wife, who believed in God and spent a good amount of time and energy I would consider talking about these issues with them. This certainly doesn't sound crazy to me, as long as you're being civil, polite, considerate etc all that jazz. [1] https://en.wikipedia.org/wiki/Ignosticism https://en.wikipedia.org/wiki/Ignosticism