Why don’t we judge each action on its individual merits instead? Why can’t we simply say “yup, this site is a problem, nothing of value lost here” without worrying about whether they’re going to block speech about whether 2 or 3 teaspoons of yeast is the right amount to put in a loaf of bread, or whether my candidate for school board is better than yours?

Let me be super clear here: nobody is entitled to use other people’s stuff to make trouble or potentially harm society. Not your mother’s house; not Facebook’s messenger. If anyone gets to use anyone else’s stuff, it is at the owner’s pleasure and under their conditions.

In some cases it's hard to tell where the line should fall. This isn't one of those.

In general you can't distinguish but fortunately that doesn't matter. Facebook doesn't block lies, it blocks "known misinformation". The information in the linked article is known to be false, and it is harmful, so it's blocked.