Another reason to kill domestic cats: If you knew how many songbirds, small mammals etc that have gone extinct since cats became the favored pet you would be sick. Do some research you will be shocked. Domestic cats (stray or not) have a huge impact on wildilfe populations especially in rural areas. For one thing, they stalk and kill prey even when they are being fed regularly.
Humans have done the same thing, are we supposed to condone killing them also? Personally I find what you to do be sick. Stray or not, extinct little birds or not, pissy smelling garage or not, that's horrible. What lesson is it exactely that you've learned? Why not enlighten us so that we may better understand why you kill people's pets?
You're a sick person and you need help.