“It is our duty to concentrate all our influence to make popular that which is sound and good, and unpopular that which is unsound (not good).”

Joseph Smith
I think what Joseph was trying to say by saying this is that every human being can tell right from wrong, and that what everyone should be doing is giving attention to what is sound and good. To what is positive and impacts us in a positive way. The negative and wrong things should have no attention and no popularity. I think he is trying to encourage us by doing what’s right so everyone can know the positive things that are going on.