Lutheran dogmatician Francis Pieper on error and truth:

The Christian Church can and should have patience with the erring and seek through instruction to remove the error. But never can or should the Church grant error equal right with the truth. If it does, it renounces the truth itself. It is the very nature of truth to antagonize error. Truth which no longer excludes error, but grants it domicile, is eo ipso resigning as truth. Pertinently Luther remarks: “Whoever really regards his doctrine, faith, and confession as true, right, and certain cannot remain in the same stall with such as teach or adhere to false doctrine.” Unionism in principle abolishes the difference between truth and error.