I feel that the moment you see a conversation as an argument at all - and that, if the other person insists on holding a wrong opinion, they care about winning the argument more than the truth - you have already lost; you are seeing the goal as convincing the other person, your goal is manipulative even if you are right.
This is a tangent, but sometimes I can't help myself.
Be wary of any idea which defines itself by what it's not.
I agree, but I think not for the reasons I'm inferring you have based on the surrounding context of this sentence.
Every idea is defined both in terms of what it is and what it's not. To have an idea and define it is to say it's something rather than not something else, since every category draws a boundary of what's inside or outside (other than some concept where you want to point to the absolute, no-thinginess of being). This is a technical point, sure, but it weakens your argument in my mind because this is true of every idea, so your argument seems one in full generality opposed to making distinctions.
I'm actually on board with this in some contexts, but I'm guessing it's not what you mean to say here.
(Unreasonably effective rationality-improving advice given the degraded state of our collective epistemology!)
Also, this reminds me of Bryan Caplan's theory of the ideological spectrum, which is that thinking of yourself as 'left-wing' is essentially expressing anti-free-market sentiment, while thinking of yourself as 'right-wing' is essentially expressing anti-leftist sentiment.
Both are defined negatively on this account, and so aren't ideologies especially composed of evidence for the efficacy of particular policies. Both would both fit a huge range of possible policies versus, e.g., the policy interventions implied by academic economics.
My favorite movie reviewer is a YouTuber named moviebob. Moviebob frequently talks about the idiotic things other reviewers are saying. I would not know these other reviewers even existed were it not for moviebob. Moviebob is a memetic amplifier for the reviewers he disagrees with.
The solution is simple: Ignore people who are wrong.
It can be worthwhile paying attention to people who seem slightly wrong because they are wrong in interesting ways. Sometimes they are even right. But you should neither take seriously nor argue with those people who value winning an argument more than the truth. "Us" vs "Them" arguments are an endless source of such people.
"Us" vs "Them" definitions make it easy to draw battlelines. Which is a problem. The first casualty of war is the truth. Ignoring people who are wrong require operating counter to our tribal impulses.
Another problem with "Us" vs "Them" is the definitions are circular. How are "They" defined? "Not Us". Be wary of any idea which defines itself by what it's not. Such an idea is usually half of a symbiotic conflict. Attach yourself to ideas that define themselves in absolute terms instead. Otherwise you end up mired in circular logic.
Circular ideas are a waste of attention. Including—sometimes—Atheism. Atheism is at its best when it is pro science. Atheism is at its worst when it is anti religion.
The easiest—and worst—way to demarcate "Us" is to define "Us" as "not Them". Speak in the positive. What are you for?