I somewhat often see people, during arguments, make remarks along the lines of: “I think that many people who hold <opposing position> do so because they’re biased.”
Regardless of its truth value, I don’t think this is a useful argument to make, for a couple reasons:
It doesn’t really address the substance of the opposing position. If you think that someone holds an opposing position because they’re biased, and you’re not as biased, then you must think that your position has stronger evidence for it. So why take the argument up a level, to people’s biases, when you can just argue about facts?
It reads like an ad hominem. Accusing your opponents of bias is a great way to get them on the defensive and cut off their line of retreat. Now if they change their mind, they are also implicitly endorsing your claim that they were biased before. So claiming that your opponents are biased makes them less likely to change their minds.
It’s defecting on the epistemic prisoner’s dilemma. Even if you feel really sure that you’re on the right side and your opponents are biased, they’re probably equally sure that they’re on the right side and you’re biased. And it doesn’t help anyone for you both to start arguing over who’s the biased one.