It is not a matter of choosing not to have children, but rather if the choice is founded on a belief that children would keep them from other things.
There is a phrase from Ignatius of Loyola that pops to mind “aversio a Deo et conversio ad creaturas”. It means turning away from God and turning towards created things. If one sees children as a barrier to the good life (what ever that may be), but still seeks sexual congress then yes that is defying the moral order. Can I assume all these people are simply forgoing sexual congress in preference for taking care of the poor, the disabled, the weak? If instead it is to have more money to go on vacation, to have a nice car, to go out with friends, then it is a turning away from God and turning towards material wants. All sin is fundamentally founded on a love of self over the love of others.