The problem you run into with that is the problem the country currently has with the lockdowns - if you require a mask, when do you plan on lifting that restriction, and what drives that decision on when you lift them? Its easy to say "we wont have it forever"....until it becomes forever. You're seeing that with states now petrified to lift lockdowns despite saying "this is only temporary" when they were put in place.
I understand wanting to keep things as safe as possible, and masks in some situations will help with that. But as you just pointed out, it isn't possible in every situation. You can't prevent illness. You can only do what you can to limit your exposure to it. That's why the main defense Disney will have in whatever policy they have is that if you don't feel comfortable coming, then don't come. Nobody is forcing anyone to come to WDW. The easy thing to say from Disney's point of view is this: these are the policies we are putting in place to keep our staff and guests as safe as possible while allowing all guests to enjoy their experience as much as possible. If you're not comfortable yet with our policies, we will still be here when you are comfortable. But for those that want to come, welcome. That's the attitude WDW, or any business for that matter, should have. In the end its up to each individual person or family to decide what is best for them or their family, without infringing on the rights of others who may feel more comfortable than you in certain situations.