Pope Pius XI, Casti Connubii (# 59), Dec. 31, 1930: “For in matrimony as well as in the use of the matrimonial right there are also secondary ends, such as mutual aid, the cultivating of mutual love, and the quieting of concupiscence which husband and wife are not forbidden to consider SO LONG AS THEY ARE SUBORDINATED TO THE PRIMARY END and so long as the intrinsic nature of the act is preserved.”
Casti Connubii is part of the Magisterium. The Magisterium teaches Catholics directly, therefore, we do not need to consult theologians who two years later all apostatized with V2.
As I said already, there is no circuмstance in which the primary ends of marriage can be subordinated to the secondary, which NFP necessarily does. If you must not have a baby you must abstain and can't risk getting pregnant in spite of your unnatural birth control scheme (NFP).