The phrase "bearing one out" refers to affirming or supporting someone's statements or claims. The antonym for "bearing one out" would be to challenge or contradict their arguments. To contradict means to deny the truth or validity of something, whereas challenging means to question or dispute it. In other words, instead of supporting someone's claims, you would be questioning the accuracy or the logic of their statements. Sometimes, it may be necessary to challenge or contradict someone's arguments to arrive at a better understanding of the truth or to avoid incorrect assumptions.