I don't think this is right. Getting sick significantly more or less can be a drawback at the individual level. Your hypothetical self-isolating people would be

I don't think this is right. Getting sick significantly more or less can be a drawback at the individual level. Your hypothetical self-isolating people would be more sickly. Most of the work humanity does against a given pathogen is in getting sick. We've recently automated that. But our immune systems are still out there fighting the good fight every cold/flu season. The ideal season for an individual is one where you get exposed but don't develop symptoms, not one where you never get exposed. Not getting exposed is like missing a ski trip-- a terrible outcome to be avoided at all costs.