This is what the current leadership believes. Tim Cook is a clearly brilliant manager. I have no hesitation in endorsing his record on privacy (and genuineness and truthfulness). However, he is mortal. The next CEO might see things differently. The unique selling point you mentioned will be on the table. There will be analysts who will crunch the numbers on what portion of prospective Apple customers will refrain from buying Apple for some particular transgression and how much such transgression will bring in additional revenue.
Apple can fend off these questions today because it has a huge chunk of the high end phone market. It would be stupid to ask Apple to do this not because it is immoral but rather because it will distract Apple from doing what it does very well: selling $1k iPhones.
"Campaign targets Apple over privacy betrayal for Chinese iCloud users"
Apple sold all their users data in China. Should that not count?
Yes in a world of infinite possibilities anything can happen, but realistically Apple is incentivized to maintain their privacy position.