Melissa Harris-Perry is indispensably resisting the ongoing effort to routinize tear gas as "harmless" "crowd control." The physiological and psychological effects of tear gas are far from harmless. The "crowd" in question is We The People, and the "control" in question is the violent curtailment of Constitutionally supported free speech and free assembly.
As I said, threats to property are usually exaggerated, and often paranoid, but Professor Harris-Perry points out that even when there really is property damage arising from a popular assembly the choice of police to harm citizens indiscriminately with tear gas is far from self-evidently justifiable -- even if prevailing media narratives seem all too eager to take such justification for granted in the name of "police protection" or stopping "mob violence."
It is far from justifiable to harm an innocent majority in the policing of a guilty minority -- although, again, prevailing media narratives seem all too eager to tar the totality of legitimate mass public protests with the brush of looting or vandalism happening at its margins. One of the reasons capital punishment cannot be justified, for example, is because the practice inevitably entails the execution of the innocent.
However, harmful measures like tear gassing are always a disproportionate response even to the reality of property crimes. International laws already forbid the use of tear gas in the policing of crowds in the context of foreign interventions. In a free society, nobody would be tear-gassed ever, because tear gas does real harm, and that real harm should matter at least as much and surely much more than the also real harm done by petty theft and petty vandalism of property -- quite apart from the fact that majorities innocent of the latter real harm are being subjected to the former real harm, which makes the bad worse, and quite apart from the fact that the former real harm tends to be exaggerated if not manufactured whole cloth in the first place, which make even worse the already bad that was already worse.
To continue the capital punishment analogy above, stealing cigars or selling single cigarettes on the street without a license may be petty crimes, and rightly so, but neither is a capital crime outside of tyrannies -- and in any society where their policing routinely eventuates in execution tyranny becomes a more readily applicable designation for it. (And I guess I'm setting aside the question of deliberate exposure to secondhand smoke as violent assault in these cigar/cigarette analogies, even though that connects up to the violence of tear gassing pretty obviously, too. Oh, well.)