This is quite related to the idea so many people have that, "Both sides are wrong. The truth must be somewhere in the middle."

This is axiomatic for some people, yet there's no validity to the supposed axiom. To take politics out of it for a second, we can look at vaccine deniers.

I follow an exchange last night in which a medical researcher was "debating" a person who called childhood vaccines risky and problematic.

The researcher laid facts on the table explaining why vaccines are critically necessary and not in fact dangerous at all.

He wasn't able to convince the hardcore vaccine deniers, of course, but I didn't expect him to since debating with "true believers" is not usually productive.

What really discouraged me is somebody speaking up to say something like, "I'm sure both of you are wrong in some way or another. As a reasonable person, I know the truth must be somewhere in the middle. So what I take from this is that vaccines are probably risky in some ways that medical science doesn't fully understand, but not as risky as alarmists are claiming."

That sounds reasonable, perhaps, but it isn't reasonable. The "reasonable" person is completely contradicted by evidence. They base their position only on the fallacy that the truth must be in the middle.