Anecdotally: I've had multiple discussions with employed, unburdened men and women (particularly women) in their mid 20s who have decided not to have children for one reason: Climate change.
The planet is collapsing. Our children are likely to die of hunger, disease, or warfare as things become more destabilized over the next 50 years.
We don't believe their lives will be better than ours, and we don't want to further deplete humanity's scant resources.
From this perspective, having children is selfish.
It may help you to travel. Some time in other continents made us realize -- we have plenty of people already. The planet will do just fine without one or three more from us.
I know many would consider it a ridiculous argument but I find your label of selfishness similar.