Yesterday I thought a little more about this. And I came to a conclusion that at least in a one weird way those who have pets are acting less selfish than those who have kids. I think so because I believe that most parents expect their kids to outlive them. But when you get a pet you are most likely to outlive them(at least in most cases). So by taking a pet home you kinda already accept the pain of losing it in the future. And doing that dispite that loss and pain is not selfish.