It is not too difficult to function in a room with tear gas, I have done it during training in the Navy. If one remains calm and doesn't rub their eyes they can see good enough to shoot back. Ducking behind the seats you could remain hidden and as the shooter approached closer you could get off a clean shot or two at the gas mask he was wearing and it wouldn't matter what body armor he was wearing. Panic is what killed most people by causing them to bunch together at the exits. There would have been time for someone carrying concealed to return fire before the gas canister permeated the room.

It doesn't matter what the gun laws are criminals will still be able to get them. The only people that gun laws apply to are law abiding citizens, not criminals. I think gun education is more important than gun laws. In areas with strict gun laws death from bladed weapons rises higher.

Even without the guns the death toll would have been very high in the movie theater if he just threw the gas canister and yelled fire but because he used guns then emphasis is placed on the guns only.

Guns are no more responsible for crime than McDonalds is for obesity, it is the people eat the food who is responsible for obesity. It is the people who use the guns who are responsible for the crime.