I don't think Apple is concerned about the <0.1% of CSAM aficionados who read about Apple's plans to scan for CSAM and thinks "hey, let me blindly trust some to

I don't think Apple is concerned about the <0.1% of CSAM aficionados who read about Apple's plans to scan for CSAM and thinks "hey, let me blindly trust some tool I found on the internet to slightly mangle my highly illegal images so that I can continue co-mingling them with personal photos in iCloud, accessible to anyone who picks up my phone while unlocked. Or any other device synchronised to the same iCloud account." The App Store is presumably full of easy to use apps which can store photo galleries in a separately encrypted vault. This is where people will go after being shooed away from iCloud, not image manglers.