If you saw a drowning child and could easily save her, you’d think you’re obligated to do so, even if it ruined your $500 iPad. If you’re obligated to ruin a $500 iPad to save a child’s life, then you’re obligated to forgo buying the iPad in the first place, and should just use the money to save lives.
This gets exactly to the heart of what morality is. The moral law being propounded here is all-consuming – if you have generalised positive obligations to others, then it immediately becomes clear that your moral responsibilities are going to dictate all your actions. There is no room to pursue anything other than morality – the moral law is a tyranny.
But if you saw a drowning child and could easily save her, do you really have a responsibility to save her? Sure, it would be nice to do so, but do you have any obligation? One of the reasons I think the Common Law is sublime is that it gets this question precisely right. It says that if you’re the child’s parent or babysitter, or you’re the lifeguard at the pool, then you have a responsibility. But if you haven’t taken up a duty of care towards the child, it’s none of your business. As Lord Keith said in Yuen Kun Yeu v Attorney General of Hong Kong (PC) 
Liability in negligence… [does not arise if a man] sees another about to walk over a cliff with his head in the air, and forbears to shout a warning.
It is confusion about this issue that is at the heart of disagreements about morality. It is why utilitarians are frequently trapped into saying that it’s wrong to love myself better than you. It is the difference between what it means to be nice – help old ladies across the road, save drowning children, wink at homely girls – and what it means to be moral – don’t kill, don’t steal, don’t break your promises. They are completely separate issues.
The political implications should also be clear. Unfortunately, in the real world there is no way to achieve that kind of government, so we cannot let the perfect be the enemy of the good.