let's look at that verse contextually
note that immediately after the salt analogy, Jesus speaks about light
salt and light are both metaphors describing how Christians are supposed to be what is best about the world
there is nothing there to suggest any sort of exception with regards to numbers or even disingenuous people
there is ONLY a positive definition of how things SHOULD be...how they OUGHT to be
the end result, is to glorify God...our Father in heaven
Matthew 5
Salt and Light
13“You are the salt of the earth. But if the salt loses its saltiness, how can it be made salty again? It is no longer good for anything, except to be thrown out and trampled underfoot.14“You are the light of the world. A town built on a hill cannot be hidden.
15Neither do people light a lamp and put it under a bowl. Instead they put it on its stand, and it gives light to everyone in the house. 16In the same way, let your light shine before others, that they may see your good deeds and glorify your Father in heaven.