I don't mean Trevor, I mean, you know, people.
I don't disagree that people assume assume negative things about people who self identify as capitalists and atheists*. But if you're talking with one of these people and feel the need to say, "I am an Atheist. But I have a strong moral core" then that's a concession to that mistake and that person will actually experience a little surge of positive reinforcement in his mistaken conception rather than feeling the uncomfortable pressure needed to change his view of atheists. At best he'll create a new small box for Trevor "Atheist. Not evil.", more likely he'll just forget and dump Trevor in with the rest of the damned, at least in the unusual situation of thinking of these things at all (atheism implies immoral), day to day, he'll likely think any atheists he knows are fine people if he happens to like them.
My impression is that qualifying some opinion you may have with, "but I'm not racist" isn't the best way of convincing the sceptical.
The term atheist is perfectly fine and those people are just plain wrong. Making concessions in how you use words firstly encourages people to press home perceived advantage but also debases language. Words don't have essential meanings but we can fight people trying to get debate freebies through misuse of language. More extreme forms of this debasement play an important role in the dystopia of 1984.
We must fight for our boxes! We must not comfort our enemies!
*(I use the atheism example here because capitalism is much more difficult to define with any precision).