Americans don't want an atheist president

The issue is as old as dirt. First of all, definitions matter. Agnostic is someone who doesn't know (if they believe) if there is a god. An atheist believes there is no god. Atheism on its face, by definition, refutes the beliefs of every other religion (yes, other religion). It's a belief system born of opposition. While most major religions have gotten relatively lovey dovey in recent centuries and say things like "there is wisdom in other faiths," atheism is inherently opposed to other religions, instead of just in particular places of holy texts like the others are to one another. If a true atheist has anything good to say about a religion, they're just trying to seem less extreme than their premises.

The most off putting thing about atheists, compared with people of virtually any other belief system, is that they seem to think they're enlightened and categorically superior to everyone else, because they don't believe in "fairy tales" or anything arbitrary and without proof. The reality is that they arbitrarily believe in one thing - that there is no god - and they have no proof for it, and that seems to govern their entire view, putting them in direct philosophical opposition to a good majority of humanity. You've got a recipe for distrust and disdain, from both sides.

A person of faith can see that scripture or whatever myth they believe to be true has gaps in narrative, or even contradictions when read in the wrong context. A lot of religious traditions can seem stuffy, or absurd. They can see these traits in other faiths as well and accept them as part of the deal when most of the relevant historical factors in your faith/spirituality/worldview happened in the neighborhood of 2000 years ago. It's a shot of humility you rarely find in the average atheist with his mouth open.

Agnostic means just that you're not entirely sure - it's perfectly fine to be an agnostic atheists which believe that there is no God, but don't know if that is true. Most atheists fall into this category, and I wouldn't be surprised if most religious do the same. And Christianity "refutes" any other religion too: I don't see Christians saying that Greek mythology or Norse Gods exist. The thing to remember here is that the definition of atheism is the belief of lack in a higher power. That doesn't mean they deny that Gods exists, nor does it mean that they hate religion. A minority of atheists actually bother to discuss religion with other people like religion was a plague - and it sadly seems like you've only met those atheists.

Second paragraph is Russel's teapot, as from Wikipedia: "[Russel's teapot] is an analogy first coined by the philosopher Bertrand Russell (1872–1970) to illustrate the idea that the philosophic burden of proof lies upon a person making scientifically unfalsifiable claims rather than shifting the burden of proof to others, specifically in the case of religion." They have a reason to not believe in any religion, because no scientific evidence is put forward from any of the religions which makes their religion true.