Also, if you can save 400 of 500 in a hostage situation and catch all the 10+ terrorists. Go for it. The terrorists would kill them anyway and if they escape, they can continue their business.
Meanwhile, if you have 5000 peaceful protesters refusing to clear out of a park, hey, so a thousand accidentally die. Meh, go ahead and gas 'em, Lou!
I think you underestimate the mindset of the police. The People had it way better when a cop needed to decide whether you posed enough of a threat to actually shoot you, and then need to justify that decision later. Now, they tase first and ask questions later. 6YO girl crying because you arrested mom? Tase. 85YO confused grannie in a panic over a situation she doesn't understand? Tase. Passenger in a car peacefully insisting you respect his civil rights? Tase.
ICAs will just make it easier for police to apply the same reasoning to large groups, rather than to individuals.
BTW, a clarification on the FP - The "unknown" agent used by Russia consisted of a fentanyl analog - An ultra-strong opiate. For reference, as high as 9% of people have a potentially fatal allergic reaction to opiates; on top of that, individuals have a wide range of responses even when given a known dose; some people can take enough morphine to kill an elephant, while others take half of a Tylenol-II and drool on themselves for the next six hours. Using opiates as crowd control will both cause needless deaths and leave a significant fraction of the crowd basically unimpaired.