The case for HV is weak. One problem is that "contraception" is never defined. Here is a definition: "A means whereby a couple has sexual intercourse with the intention of not procreating. Notice the word "intention". HV never considers intention, which is a major flaw in moral theology -- one must always consider intention when dealing with the morality of an act. 

I believe that the reason for the omission of a definition of contraception and a consideration of intent is that it shoots the support for NFP in the foot. Under my definition, NFP is most certainly a contraceptive method. It is practiced by couples who want to have intercourse, but do not want to conceive. Otherwise, why would they bother with it?

HV also says that it is based on natural law. The magisterium knows this because it knows what natural law is. How does it know this? It knows because the magisterium says it does. "We know this is true because we say it is true." Circular reasoning at its best.