If you were to try and kill me with a knife, your life is on the line as well. If you try to kill me with a drone, your risk is only the money and time spent on the drone. There is quite a difference.
I'm unclear as to what the moral difference is. It's more moral to kill someone if they can fight back? Then why are we giving our soldiers tanks? Guns? Fighter jets? Knives?
The difference is the cost to yourself, or people you care about, when you want someone dead. Popular sentiment turned against the Vietnam war in the US because Americans were coming home dead, not because of the Vietnamese that we were killing. When we eliminate the cost of war, we make it more likely to enter one, and stay in one.
Yeah, the American populace might not care, but the victims do care, and how upset they are made directly affects all other efforts in that area. Peacemaking and nationbuilding only gets more difficult the more people that have lost family members to the invaders.
If we'd gone into Baghdad WWII style, carpet bombing and all that, we'd probably still be fighting a significant war in Iraq. Or the country would be depopulated. Presumably the appearance of ISIS was largely a reaction to western actions in the region, and its initial strength was proportional to the outrage that could be drummed up. Sure, there are probably asinine military commanders that don't account for this, but it isn't the universal rule.
Why not just send them in with their fists.
This line of reasoning has no rational basis.