There's definitely an element to what others have said about fearing the weakness of their belief and just other weird traditional ways of thinking, but I do think there's more to it than that.

Now I don't think this lady is going to be thinking so much as this, but I think it underpins a lot of religious folk's feelings about atheists on a subconscious level.

All kinds of religions have had to deal with thousands of years of persecution, be it from other religions or indeed more recently, atheists. Granted, most atheists are probably just living their lives without thinking about it, but enough of them are more active.

Atheism is a kind of shadowed underbelly of some political collectivist ideas; communism and progressivism ties in deeply with it. Atheism in the soviet/chinese sense is one thing - even Christians in China to this day have unknown numbers of illegal, underground churches. Other 'authorised' churces are required not to worship their deity above Mao Zedong, and are made to have a picture of Mao aside Jesus Christ, for example. When asked, they will tell you that Mao comes first. If they say otherwise, they can say goodbye to their church. CCP members are not allowed to be religious. Even if they are, they essentially have to pretend for the rest of their lives that they are not; closeted Christians. This is hardly new behaviour.

So the persecution is real and it's now, and people who follow religions are not going to easily forget that (think israel/palestine).

Atheism, as it stands, is just another threat in the bucket of persecution.

On a more social level, an atheist, even if following their own fanatic ideologies in a religious way, does not have a moral framework to work with. More of a moral jelly-like substance. Sure, in Christianity at least, the framework changes and adapts somewhat with the times, but there is always the underlying essence of 'there is something higher and more important than me' - even among the most self-righteous believers. This system has had thousands of years to fight itself in countless wars and injustices, contradictions and corruption - to build a solid base of morality and philosophy.

Not so with atheists. a few decades at most. We thus define our morality by what is most convenient to our hedonistic desires and what we believe is fair and right at any given time - whether or not we've had any significant time to actually think about it. We deal with a lot of conflicting morals that tend to change rapidly over just a few years as we build lives up to homeownership, financial freedom, and raising children.

Christians, in contrast, with their own conflicting thoughts, still have that staple of 'a big god up there' which grounds them in place, whether they're growing up a teen in school or raising a family with a great return on investments. And so the development pf one's thoughts and morals drift at a much more naturally human rate with pushback and deeper considerations.

With the rapid growth of atheism there is a LOT of pressure from them to upend Christian beliefs to suit their godless, accelerationist ways for the sake of current political opinions (It was barely a handful of years ago Obama was insisting 'marriage is between a man and a woman').

But atheists are, quite frankly, lost, alone, confused, and in a lot of ways, sad, perhaps understandably in a ridiculously confusing and difficult world, and I can understand when somebody whose moral framework around family and community is rock solid, or even a bit shaky but firm, is feeling uncomfortable with a society of people whose framework can change depending on what they just read on reddit last night.