Interesting topic and the question of where to draw the line in terms of selflessness vs selfishness is something I have been thinking about a lot the past couple of years. In the end everybody pretty much draws the line to the point it makes them feel comfortable and arguments also go as far. I don't mind pets myself even though I don't have any myself right now. You can go a step further when it comes down to your argument about that the cat is from a shelter and it would have died. What if you let the cat die, not support the meat industry by having to buy cat food and use all the money you would have spend on it to actually save the lives of kids in afrika. Is that not the more ethical thing to do purely from a though experiment angle ?