I'd concur with's answer from the perspective of the individual's day to day… As a parent, there is less absolute time in the day for "self care".
Philosophically, the question becomes much more difficult – is the childless person concerned about population growth worldwide, more than having time to play Batman: Arkham City uninterrupted? Is the parent concerned with continuing their genetic pattern, or other form of legacy?
I have known childless people who were demonstrably unselfish people. And I've known parents who had kids as a way to avoid being alone, or to help prove some point about their own self worth.
Overall, I'd say the question cannot be "fully answered" in the general case… Though perhaps the question "is it more harmful to be selfishly childless or a selfish parent?" could be more definitively argued.