violence and rioting should never be allowed.
This nation was born of 'violence and rioting'. It's because we 'broke the law' and fought the enforcers of our oppression that we now exist as an independent nation. And when the founders declared to the rest of the world why they had done so, and the principals of the new nation they intended to create, they specifically stated that if that new nation were to become a new oppressor of the people, the people have the right to rise up again, and remove the shackles that intent to bind them.
As our current government has once again become corrupted by the wealth and greed of an elite few, and is being used to subjugate, exploit, oppress and abuse the people once again, the people are feeling the need to rise up, yet again, and fight to overthrow the tyrants, and end the tyranny. And our founders would approve. They even said so in their written Declaration of Independence.
So you are quite wrong to presume that there is never an appropriate time for violent rioting.