but i still think you should be allowed to carry pepper sprays

One of the dead girls was carrrying a large pair of scissors for self-protection, you can't rely with confidence on any weapon saving you from a dangerous situation. You can make your own pepper spray from peppers and water or import mace illegally, or make do with a dog repellent spray which are legal and do much the same.

Too much capsaicin can cause death. Too little can fail to incapacitate an assailant. The Scoville scale si a good indicator of how much ground pepper to use, the higher the figure, the hotter, more dangerous it is.

"Capsaicin is also the active ingredient in the chemical riot control agent pepper spray. When the spray comes in contact with skin, especially eyes or mucous membranes, it is very painful."
 http://en.wikipedia.org/wiki/Scoville_scale#List_of_Scoville_ratings

Spraying mace/pepper spray/dog repellent in anyones unmasked face will drop them and render them helpless, like "having your face drenched in gasoline and lit on fire", and could be used against you. If you want to make your own, don't follow internet recipes which are often intended as insecticides and can be too strong. If you don't intend killing someone and don't have a chemistry degree, there is one way to get the right strength without risking harm to others - try it on yourself. Add a small amount of the strongest pepper you have to a few litres of water. Use a garden sprayer to spray it in your own face. If it is merely irritable, add more pepper until 'it is like having your face burned'. It may be masochistic but it's more moral than testing it on anyone else. Then add a little bit more for luck, bottle it in empty pump aerosol devices, label them 'Garden Insecticide', and pass them to your friends. They work on insects too while not harming plants.