I have been reading about abortion recently and came across a ‘thought experiment’ used by Judis Jarvis Thomson about an expanding baby. The scenario is that you're in your house when your baby starts expanding rapidly. You realise that you have no chance of getting out and the only way to survive is to pop and kill the baby. The idea is that this is an analogy for mothers who will die if an abortion is not performed i.e. is it ok to kill in this form of self-defence? These thought experiments are designed to provoke a moral attitude which can then be applied to discover your true feelings on a particular issue. My instant reaction was that yes, it was ok to pop the baby in order to survive and therefore I believe abortion is ok if it saves the life of the mother. However, imagine that the baby is now an analogy not for abortion but for a virus like AIDS, by the same thought experiment it could be argued that saying yes would justify killing everyone who had AIDS in order to save everyone else in the population. Killing in a form of self-defence. This clearly would not be moral. My question is then, how accurate are these thought experiments if the same answer can provoke the same gut reaction, lead us to the same argument which can be applied in two different situations, one of which is arguably moral and the other which is completely, undoubtedly immoral?