“if seat belts work, why can’t I drive drunk?”
That would assume one knowingly infected and symptomatic intentionally exposes others.
Work on a better metaphor.
People who drive drunk often vastly misjudge how impaired they are. If they realized how impaired they were, they would make another choice, but they believe themselves to be unimpaired and get behind the wheel.
It’s a perfectly fine metaphor. It doesn’t assume malice. Just a certain level of shirked responsibility for taking reasonable precautions to preserve human life. Every one of us has a moral obligation to make all reasonable efforts to preserve human life from conception to natural death.