It's worth noting here that tear gas is generally prohibited to use during wartime. Bunch of treaties that countries have signed forbids the usage of tear gas.
But, seems what's not fine to use in war against enemy combatants, is fine to use against your own people in order to control crowds of people. Something here feels wrong, if it's put like this.
I'm neither agreeing/disagreeing with you, just worth noting how the rest of the world considers tear gas.
(Nb I don't intend this as support of any particular actions by the police lately)
Once you release chemical weapons, you can't control them, they go wherever the wind takes them. This could be in the direction of civilians or friendly troops.
Here in Seattle they used so much tear gas in Capitol Hill last night that it was seeping into homes. A coworker reported that his 3 month old child woke up coughing like crazy.