I mean, the fact that he only takes issue with it when he finds out about the minority reports kind of makes sense. When you think the predictions are 100% accurate (a conclusion that is supported by the fact that murder has been eliminated) then it's easy to believe that people, especially cops, would prioritize stopping those crimes over the moral concern of imprisoning people who were 100% guaranteed to be about to commit murder, even though they hadn't actually done it yet. As soon as you find out about the minority reports though it throws into question how certain you can really be that they were actually going to commit the crime, and all of a sudden you're not imprisoning people who were definitely going to commit murder, you're imprisoning everyone who might have committed murder, which is much more morally problematic.