If you require vaccine passports for certain activities, you are punishing the unvaccinated by not allowing them to do those activities. I think a better strategy would be rewards for getting vaccinated since the punitive strategy may lead to people digging in even more.
It's just marketing, the mechanism is the same either way.
It's like a gas station that charges extra to use a credit card. That's the punishment stick for using a credit card, and probably not allowed in the credit processors agreement.
So, instead they offer a discount when you use cash, and advertise the cash discount price on signs. Now it's a carrot for using cash.
Between the two, nothing changed at all. It's the same 2 prices and the credit card one is higher.
A vaccine passport would need good marketing to show it as a carrot for vaccinated people instead of a punishment for unvaccinated. Either way, the mechanism is the same, vaccinated people are allowed something that unvaccinated are not.
Let me try a different analogy that works better for adults. To me, a reward is get vaccinated and get a free admission ticket to Animal Kingdom. A punishment is if you don't get vaccinated you aren't allowed to purchase a ticket to Animal Kingdom. The latter is what a vaccine passport would be.
Change the Animal Kingdom ticket price to $10,000 and offer a $9,900 discount for vaccinated people. Same effect, nobody (or not enough to matter) is going to pay the full price.
Just like, is the Dole Whip a reward for not punching your sibling or is not getting it a punishment for punching them? Same effect, it's the marketing that's different.