How can one argue against people with antibodies and/or recovered from COVID-19 NOT WEARING A MASK based on this sign?
Because a lot of people will wear a mask a place that everyone is, and won't wear one in a place everyone isn't. Like it or not, humans adapt to their environment greatly based on assumed peer pressure and a desire to fit in. A lot of people feel very funny wearing a mask in shul when they are the only one doing so. Being as such, I feel an obligation to not be one adding to the environment and norm of not wearing a mask, even though I may be fairly confident in my personal non carrier status. Sometimes being part of a community means doing things that you personally have absolutely nothing to gain from, based on al tifrosh min hatzibbur. That can mean davening in your shul even if timing is inconvenient for you at a certain minyan and you have better options available, attending certain shiurim to be mechazek even though you personally don't gain much from it, and wearing a mask to perpetuate an amosphere, even though it's personally irrelevant to you.