In the literature on conspiracism, fundamentalism, and extremism, we find so-called vice explanations for the extreme behavior and extreme beliefs that they involve. These are explanations in terms of people’s character traits, like arrogance, vengefulness, closed-mindedness, and dogmatism. However, such vice explanations face the so-called situationist challenge, which argues based on various experiments that either there are no vices or that they are not robust. Behavior and belief, so is the idea, are much better explained by appeal to numerous situational factors, like one’s mood or how orderly one’s environment is. This paper explores the situationist challenge to vice explanations for conspiracism, fundamentalism, and extremism in more detail by assessing the empirical evidence, analyzing the argumentation based on it, and drawing conclusions for where this leaves vice explanations. The main conclusion is that vice explanations for such extreme behavior and extreme beliefs need to be fine-tuned on various points, but that there is no reason to think that they have been discredited by empirical evidence. Moreover, the situationist challenge shows that sensitivity is needed for distinguishing when vice explanations for conspiracism, fundamentalism, and extremism are appropriate, when appeal to situational factors is more fitting, and when the two can be combined.