If this is a conversation being held in good faith, and you impute to your nominal opponent a position that you believe is better than what it turns out they actually meant, then they have an opportunity to respond in ways other than simply taking (21st century) offense at your mischaracterization. They can correct you in a followup. Or they can discover that they appreciate your own iron-cladding of their argument for them and adopt it for themselves. At the very least, unless they're on a hair-trigger for being offended, at which point basically by definition they're not arguing in good faith anyhow, they're not terribly likely to be upset that you have granted them a stronger position than you believe they successfully argued for; from a human perspective it's still a demonstration of positive intent, even if the direct manifestation was misguided.
It's not a static situation, and most of the outcomes are still better than if you drill down on some particular issue they have and play the "gotcha" game. (At least, better if your goal is authentic intellectual conversation.)
It's not a static situation, and most of the outcomes are still better than if you drill down on some particular issue they have and play the "gotcha" game. (At least, better if your goal is authentic intellectual conversation.)