The call it paste, sounds better I guess, than acid that burns a hole in flesh. You were very contentious about what you were doing but I'll stick with any method other than this one.
Because they can badly hurt you or other cows intentionally or accidentally with those horns once grown. This was a bull calf that went on to be a herdsire. No one wants an already potentially dangerous bull to also have horns. I don't dehorn anything I intend for meat within 18 months. But if they are going to be handled and live a long time, they get dehorned.