All humans eventually die, and most natural deaths are far more horrifying than how we would be able to murder other humans, especially in modern times (though even traditional slaughter is nothing compared to dying of cancer, stroke, being murdered in a car crash, etc.)

So, I think that it is important how the humans are grown (prisons are absolutely horrible, unacceptable places to live in, and should ideally become illegal sooner rather than later, regardless of the consequences on the price of labor). But I really don't think there is any reason to feel bad about the murder of 25 year old people who have led a decent life, even if it may be shorter than they would expect in nature (the huge proliferation of the human species is kind of payment for that, in a way).