You are correct, if Amazon Go stores end up being targets for robbery that would damage roll out of additional stores the problem is that I can't think of how any one could rob them blind. The primary problem being that there is no cash to steal in the store and the goods all have low price to bulk ratios making them just plain difficult to steal. They just aren't worth robbing. Not that someone won't try anyway.
That isn't to say they couldn't be targeted by shoplifters, but that is a huge difference from being robbed blind. And even here the store has two advantages in that login with the app is required to even enter and the whole store is covered with sensors and cameras in addition to the staff.
As for the PR fallout I'd actually be interested to see how that goes, how much biometric data Amazon was able to gather on them even with a mask and/or bulky clothes, how the security features of the store actually work.