Sometimes the person you disagree with is badly informed. Sometimes they are dishonest. But assuming one of those explanations every time is a convenient way to avoid understanding what the disagreement is about.
Two people can read the same evidence carefully and still reach different conclusions. Before deciding that one must be stupid, it helps to ask what each thinks the evidence establishes and what each cares most about.
What kind of disagreement is it?
One possibility is a factual mistake. A statistic has been misread, a claim isn't supported, or an inference doesn't follow. Better evidence may resolve that, although persuading someone to admit an error isn't always easy.
A second possibility is social pressure. People may accept an opinion because disagreement would cost them friendships or standing within their group. That can explain why they hold it without proving that the opinion is false. A socially convenient belief can still be correct.
A third is a difference in priorities. Two people can agree that a policy increases security and restricts liberty while disagreeing about whether the trade-off is acceptable. They haven't necessarily misunderstood the evidence. They value the consequences differently.
There is also the information available to them. Funding, editorial decisions and institutional habits affect which questions get investigated and which findings receive attention. That deserves scrutiny. It doesn't justify dismissing any inconvenient finding as propaganda.
These explanations can overlap. They aren't four boxes into which every argument will fit neatly.
What could evidence answer?
It helps to distinguish a question about what happens from a question about what ought to happen. Did a policy raise wages? That can be investigated. Was the benefit worth a restriction on someone else's freedom? Evidence informs the judgement, but it can't make the choice of values for us.
Treating a factual question as a matter of preference lets people ignore evidence. Treating a difference in values as a factual error can leave both sides waiting for a study that will never settle it.
A more useful conversation starts by establishing what each person would accept as evidence and which consequences they consider most important.
Thinking independently requires checking yourself
There is value in becoming less worried about whether your friends agree with you. It also creates a responsibility to examine your own reasoning more carefully. If the people around you aren't challenging it, you need to look deliberately for evidence that might.
Noticing bias in an institution doesn't make you immune to bias yourself. Nor does distrusting a consensus establish that the opposite view is true.
We won't resolve every argument by sorting these distinctions out. We can at least stop calling a difference in priorities an inability to understand the facts, and stop treating a factual mistake as though everyone is entitled to their own answer.