You don't have to have every student in a class acting up to get the field trip cancelled.
You don't have to have every insured have an accident to have rate go up.
You don't have to have every citizen supporting an evil regime before you can attack that country.
You don't have to have every every person in an epidemic zone to be infected before quarantining everyone.
It is simply the Left running defense for the terrorists to even make this false "can't punish them all unless they are all guilty" theme.