Moral properties are natural properties
There's no natural property or set of natural properties which are synonymous with "good" or "bad" - good and bad are judgments we make of natural properties and so can't be identical to these natural properties. Saying pleasure is good is not the same as saying "pleasure is pleasure" and so can't be identical.
If moral properties are identical to natural properties, it suggests that resolving moral dispute is a matter of just knowing more empirical facts. But people can disagree about whether something is good or bad and still agree about all the natural facts. So moral properties can't be the same as natural properties.
One can't think something is wrong but also not be motivated by this judgment (judgment internalism). But if moral judgments amount to merely claims about what natural facts will occur, then it seems like someone could be indifferent to these facts obtaining. But this is implausible, as anyone that judges x to be good should be motivated at least somewhat to achieve x.