I recently came across a question asking that in a hypothetical scenario where a doctor has to decide either to save a woman giving birth or the baby birthed. In most of the comments to the question, most people said they would save the woman instead of the baby. Shouldn't saving the baby be morally right as it will live longer than the woman? Furthermore, some utilitarian ethicists believe that it is not that bad to kill babies because they aren't fully conscious like adults and so they aren't "persons". However, the problem with this logic is that these babies will eventually become "persons". If you think about it, saving the baby leads to greater total lifespan and higher average lifespan. So why do most people - even utilitarian philosophers- believe the adult's life matters more than the baby's?
I'm not so sure that the total amount and aggregation of "happiness" would be increased if the baby is saved.
It's probably true that saving the baby would generate more happiness, because they will be happy for more time than the adult would have been.
However, I think it's also true that allowing the adult to perish could result in significantly more suffering due to all the people that have a personal relationship with them.
I also think that avoiding suffering is much more important then creating happiness. So, while I'm happy to create happiness, I am hesitant to trade the expected average happiness of a future person for the suffering of all the adult's friends and relatives.