Oh, I guess I misunderstood. I read it as "We should survey to determine whether terminal values differ (e.g. 'The tradeoff is not worth it') or whether factual beliefs differ (e.g. 'There is no tradeoff')"

But if we're talking about seeing whether policies actually work as intended, then yes, probably that would involve some kind of intervention. Then again, that kind of thing is done all the time, and properly run, can be low-impact and extremely informative.