If it becomes an obligation to help others, this seems to take away from people's agency. Surely if we must always choose the act that helps others rather than a selfish one, you could justify never eating full meals when you could use the money to buy meals for others, or never getting an education when you could be building a shelter in another country. Thus, if everyone was obliged to help others all the time, no one could be justified in furthering themselves, and advancing society. If sacrifices should be made for the long term, surely it is better to sacrifice the hopeless poverty stricken people to advance science and other fields of society, rather than always sacrificing the modern lifestyle we've created and regressing to help poor people who will always exist no matter what we do (homelessness from natural disasters is unavoidable for example).