Explaining the legitimacy of demonstrating in Islamic Shari`ah

Explaining the legitimacy of demonstrating in Islamic Shari`ah.
The prominent Saudi Scholar, Dr. Muhammad al-Ahmari states:

Holding demonstrations to support the truth and refuse injustice, oppression
and corruption is a legitimate recurring act that Allah sanctions in
condemning corruption as well as in celebrating feasts. Examples of this are the
Prophet's demonstrating (with the companions) to bid farewell to the Muslim
armies as well as to welcome them when they returned. Another example is during
the conquest of Makkah. The Prophet (peace and blessings be upon him)
commanded his uncle Al-`Abbas, to show Abu Sufyan the strength and power of the
Muslim army as they were marching towards Makkah with their banners raised. By
commanding them to do so, the Prophet wanted to convince Abu Sufyan that he
could not confront the powerful army of Muslims.

If we cannot at least express our voice, display our position, and declare
our sympathy with our oppressed fellows, as well as show our readiness to
protect our invaded and occupied lands, then what does remain for us to do?
Hence, explaining and supporting the truth as well as confronting and condemning
injustice and corruption by all possible means is a legitimate recurring right
in Islam.