Unfortunately, your interpretation of facebook's motives require trusting that they'll only do what their PR says they'll do, and not what they're able to do. Or, even if that is their current reasoning, one then has to trust that they won't then take advantage of said ability in the future.
For many of us, facebook's past actions are more than enough to prove that they do not deserve the benefit of the doubt in this case.
In addition, if this is indeed the backstory, then Facebook’s product management team failed miserably by not owning the story and instead deferring to anonymous internet commenters to explain their changes.
Remember when Facebook Security added SMS 2-factor verification and promised to never use the phone number for anything else, but then they were overridden and it was fed into the social graph, leading to their CISO resigning ?
For many of us, facebook's past actions are more than enough to prove that they do not deserve the benefit of the doubt in this case.