An absurd opinion is probably a misunderstood opinion.

If somebody whom you’ve known to be generally reasonable in the past suddenly takes up with some damn fool notion that nobody in their right mind would believe, then . . .

. . . you’ve misunderstood something about their position . Either you are incorrect about their stance, or they believe different facts than you do, and hence are drawing their conclusions from a different place than you are drawing your own. A simple misunderstanding of this type will be the case 999+ times out of a 1000. The fix is to go have a quick conversation with the person in question. That conversation is a pattern (a template solution for a common problem), and it will educate one or both of you very quickly. Wailing about the stupidity of the other person’s presumed opinion is an anti-pattern that wastes time and creates bad will.

Absurd opinions = misunderstandings to be surfaced and resolved. Bank on it. Act on it.