Say what one will about guns, knives, cars, trucks, bomb making material, etc. That stuff can be banned from the Earth. But unless men repent, give up their evil thoughts, give up listening to false teachers telling them to kill everyone who doesn’t submit to a certain religion, etc., there will still be evil among us!
The problem is the heart and if that doesn’t change, the evil doers will still find a way to commit horrible acts (Matthew 15:18-20). Repentance must be personal, beginning with people looking at their lives to see if the way they live compares to the values of the word of God (Matt. 7:12). So to the person thinking about going on a murderous rampage. Don’t! That is Satan trying to convince you to do a damnable act. Resist him. Change your life, quit the evil thoughts and seek God.