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.
Don't you want to live in a world where people make decisions based on observable things, rather than blind faith in arbitrary nonsense?
You can't reason with a religious person. Their axioms can be completely incompatible if, for example, they believe the afterlife is more important than actual life.
For me I was a kid and approaching confirmation in the Catholic Church and realized I didn't believe in any of it. The conclusion was that I don't think there is any reason to believe in the existence of a god or gods so I don't spend my time worrying about them.
The rest of your rant is getting confused between anti- and a-. There is nothing negative or combative implied by a-theist that there is with anti-theist.
It's pretty clear that the cultural position of religious organizations in many places has lead to enormous and enduring harm. Which is particularly galling given their claims around morality. Whilst this is true for non-religious organizations as well I won't give religious organizations a free pass because it opens up a claim of being anti-theist or an uppity atheist.
Perhaps the "Western tradition" is European Christianity?
There is a western tradition wherein atheists are considered untrustworthy men, as no matter how different or foreign someone is to you, if you can agree there exists a god (by whatever name) who rewards good and punishes evil, and that some intentions of this being have been revealed, this belief is a foundation for a basic level of trust that transcends language.
The whole atheist enterprise is premised on an "anti-" identity, where the "-ist" person evaluates their own identity against a perceived reflection of this divine straw-man. A recent pope described "hell" as being "the absence of God," I suspect atheist hell is the absence of someone to hector with tedious hypothetical arguments. The anti- identity is what we used to call being a punk, or someone who identifies as exempt from the scale of "good," because they perceive themselves as having been victimized by the bearers of that standard, and they look for others to seduce with a misery-loves-company sympathy. They're people you tolerate and have compassion for, but don't take as much risk to invest in. Whether or not one agrees with the morality of that, it's a summary of the very roots of what we call western civilization.
Edit: removed some snark.