Earlier quoted context omitted.
No one "forms their own opinion" in a vacuum. Your beliefs and opinions are influenced in a multitude of ways by your environment including the media you consume. Asking how the biases you have were formed is something everyone should be asking of themselves, and certainly doesn't seem like an inappropriate question.
Problem is that it's a subtle accusation of speaking in bad faith or an accusation of lacking agency. In order to have respect for the other person, you can't start from either of those positions.
We have to be able to ask these questions and assume they’re not attacks to have productive dialogues.