Argue against a decision I'm leaning toward

I'm leaning toward this decision: [Decision] Make the strongest honest case against it. Don't balance it with the case for it; I already have that. - What am I assuming that might not be true? - What's likely to go wrong, including effects that only show up months later? - Who would object, and what would their best argument be? - What would have to be true for this to be the wrong call? End with the one or two risks that matter most, and how I could test them before committing.