> The officer should still have discretion here to let someone go if they don't feel the person is impaired. But giving them a number means they can't use that discretion the opposite way, e.g. arresting someone because "they seem like they're driving high". I imagine that kind of discretion would disproportionately affect minorities, so I see this as a win.

I can't imagine a situation where an officer would employ the use of a breathalyzer and we worry about discretion. The officer used their discretion to pull the motorist over. They used their discretion to perform a sobriety test. They used their discretion to employ a breathalyzer.

Point is, if the cop wanted to let you off there are numerous occasions to do so.