Lincoln told grant to insult people, he made the right call
A) I doubt Lincoln said that, or if he did, you have totally left out the context that would justify that remark.
B) Insults invariably set up opposition and that leads to conflict not resolution. How can that be helpful?
I certainly insult my share but none of it is unprompted. If I can communicate with someone without insulting that person the results are so much better. You should try it if you suddenly feel like acting less like a child.