The reality is that if you put the pros and cons down on paper you will always find a reason not to have them. If that's how you think then no don't have them.
You want reasons that are not selfish. Understanding the relationship with children that a parent , either biological or adopted is not something that can be quantified in the way you are reasoning. However the best way I can explain it is it turns you into someone who would instantly put another in front of their own wellbeing. In most cases this leads to something similar to what economists refer to as asset community ownership. You start putting something further into the world. As little sometimes as stopping another child running into a road instinctively. Sometimes larger.
Secondly , you are viewing that child as an automatic extension of your they aren't. I don't know what my two DC will bring to the world. I believe I am bringing them up to bring something positive. They will go their own way and do what they choose. You cannot quantify what people in the future bring to the world. It could be big things like curing cancer. They could be the next great thunberg. Or they could simply one day complete an action that helps another. A child always has the propensity to bring good to the world. You don't know what this is , you may never see it. However the truth about parenting is you put years and effort in and you may not see the impact your DC have on the world.
Honestly though if this is the way you make the decision you are simply not ready. Nieces and nephews and even teaching are not in any way practice for parenting. Teaching is laudable and hard but it's not the same as becoming instantly responsible for everything about a baby. Their health , their wellbeing , their development , their social interaction, teaching them morality and resilience and doing it 24 hours a day for 20 odd years. Would he give his life , his everything for every child ? Well no of course not. Nor should he. That however is the commitment of parenthood. Once you are in , you are in. No get outs. No changing your mind.
Look if he has made this decision o what sounds like cerebral reasons he is not ready for the emotional roller coaster and sheer grit and determination it takes to be a parent.it is unutterably worth it. A single smile as a baby and you would fight the world to protect them in a heartbeat.
It is also relentless , exhausting , frustrating and thankless. Logic doesn't work here because the reasons are far more esoteric than most of us can communicate. Me included.