A principled person would treat everyone fairly.
Anger, in general, is caused by trauma. As mentioned above, atheists tend to fit a specific demographic:
https://www.pewresearch.org/fact-tank/2019/12/06/10-facts-about-atheists/
Among that demographic is 68% male, 78% white and 43% with a college degree. The study doesn't break out the "angry atheist" but likely have the same demographics with the addition of "100% immature". This would go with anyone who is perpetually angry regardless of choice in beliefs, both spiritual and secular.
In the U.S., atheists are mostly men and are relatively young, according to the 2014 Religious Landscape Study. About seven-in-ten U.S. atheists are men (68%). The median age for atheists is 34, compared with 46 for all U.S. adults. Atheists also are more likely to be white (78% vs. 66% of the general public) and highly educated: About four-in-ten atheists (43%) have a college degree, compared with 27% of the general public. Self-identified atheists also tend to be aligned with the Democratic Party and with political liberalism.