In America the Constitution and Bill of Rights is the highest law of the land. The Constitution and Bill of Rights guarantee basic rights, freedoms, and due process to all Americans, regardless of race, religion, national origin, sex, authenticity, age, sexual orientation, etc. There are many bases upon which discrimination can be found other than race alone. One of the greatest blessing bestowed upon America, through the Constitution, is freedom of religion. Each of us if free to seek of God of our own understanding, rather than being force to conform to a dictated state religion (eg theocracy).
Because of the way America was governmentally structured, we are a diverse people, with each divergence free to honor its own heritage; yet the common denominator that hold us together is that we are all still Americans. Different groups celebrate different holidays, for example. This is only right, and each of us must come to respect the differences among the diverse members of our society. It is the American way.
I see nothing threatening in a meeting of black mayor. This allow the black mayor to network together to share experiences, best practices in governing, common problems and possible solutions, and they are free to do so. It is a win-win proposition, where the mayors win, their constituents win, and all Americans win.
Regards,
LelandJ