Amendment VI of the US Constitution reads:
In all criminal prosecutions, the accused shall enjoy the right to a speedy and public trial, by an impartial jury of the State and district wherein the crime shall have been committed, which district shall have been previously ascertained by law, and to be informed of the nature and cause of the accusation; to be confronted with the witnesses against him; to have compulsory process for obtaining witnesses in his favor, and to have the Assistance of Counsel for his defence.
Being able to confront those who make complaints against you is a fundamental part of our judicial system and an important one. Once you allow anonymous complaints to be the basis of government action against citizens, you open the door for all sorts of abuses.
This isn't a criminal prosecution.