Is it permissible to show harshness to one whose harm is feared, and what are the controls for that? And what should be the demeanor of the believer when walking?

It is permissible to show harshness to one whose injustice is feared, in order to prevent him from audacity. Wisdom dictates placing severity where it is due and leniency where it is due. The one who enjoins good must adhere to the Islamic etiquettes, except when there is a need for deterrent force against oppressors; as Allah Almighty says: "And do not argue with the People of the Scripture except in the best way - except for those who commit injustice among them," and the Prophet, peace and blessings be upon him, said: "Whoever among you sees an evil, let him change it with his hand." In walking, humility and avoidance of arrogance are required; as Allah Almighty says: "And Allah does not like every arrogant boaster," and His saying: "And the servants of the Most Merciful are those who walk upon the earth easily." The Prophet, peace and blessings be upon him, also forbade rushing to prayer and enjoined tranquility and dignity.