Controversy is essential where precious truth is rejected or distorted. And controversy is deadly where disputation about truth dominates exultation in truth. The reason controversy is essential in the face of rejection and distortion is that God has ordained that the truth be maintained in the world partly by human defense. So the preservation and transmission of precious truth from person to person and generation and generation may require controversy where truth is rejected or distorted. It's deadly also because it focuses on the reasons for truth rather than the reality behind truth, and so tends to replace exultation in the truth with disputation about the truth.
Controversy tends to threaten both love and praise.
It's hard to revel in a love poem while arguing with someone about whether or not your sweetheart wrote it. So controversy is essential in this fallen world, and controversy is deadly in a fallen world. We must do it and we must tremble to do it. A wise counselor for us in this is John Owen, the Puritan pastor from 340 years ago. He was involved in many controversies in his day - theological and denominational and political.