A rebuke goes deeper into a man of understanding than a hundred blows into a fool.
Proverbs 17:10 ESV

If you give people the benefit of the doubt, they might disappoint you, but it's still simpler for everyone. If you start by assuming that the other person is a fool, then you'll make an enemy if you're wrong and probably not accomplish anything if you're right. If a friendly rebuke is enough to prevent further harm, then all's well.