https://www.washingtonpost.com/news/morning-mix/wp/2014/08/1...
(Of course we can discuss if most of the uses of tear gas are wrong, but lets for a moment think that we have a moment were we need to chase away a crowd of evil persons riotong and threatening to kill perfectly innocent children.)
But, we have de-escalation tactics, riot shields, smoke canisters, and literally guns.
If an officer wouldn't fire a gun, I think he shouldn't use tear gas.
Imagine a scenario where a small group of cops is watching a peaceful rally. You and your family are part of the rally. Now, a subgroup of the people near the rally start to pelt the cops with bricks and rocks. The cops are surrounded and wildly outnumbered. If de-escalation does not immediately work and the cops have a less-lethal means of response, they should use that initially. If you deny them all the less-lethal means, they're going to use lethal means to defend themselves. You and your family are now in the area where copper bullets are flying because you didn't want the cops to have tear gas.
I'm sure being tased sucks. I know tear gas sucks. I'm also pretty sure both suck a lot less than being shot and that the Taser company and police use of tear gas have saved lives.