That isn't the argument at all. What Apple can't have happen without major reputational damage is get caught doing it without telling its customers. Thus this

That isn't the argument at all. What Apple can't have happen without major reputational damage is get caught doing it without telling its customers. Thus this is seen as a marketing backdoor to the actual backdoor. This is seen as a ploy that later gives Apple the plausible deniability argument that the government is making them do it (other forms of content) even though they created the means (on device scanning) for the government to exploit. Why limit it to content that will be uploaded to iCloud? Why limit iMessage scanning to kids? Why not also let the government know? Why limit it to child porn since the system works for any image? Why limit it to 30 hits?