I began to suspect that Catholicism101 and Allmonks were the same person. I'm not convince that they aren't, but they both joined CI just to chime in on this debate. I'm not sure what their angle is, but they're clearly Ibranyites or Dimondites (or possibly even the Dimonds themselves?!).
First of all, if what Pius XII taught in his address to the midwives is "heresy" then he doesn't get let off the hook for it. He loses his office because of it. So let's get that clear. He doesn't get to be a public heretic and the pope, the Church has NEVER, EVER recognized non-Catholics as being able to hold office. Ever.
Furthermore, they seem to be completely ignoring, as SJB said in another thread (the one bowler started as a distraction when he lost in this thread), the difference between a singular act which may be sinful and a continued course of actions which may be sinful.
I really have nothing else to say on this issue that I haven't already said. In Pius XII's address to the Midwives he taught:
1) He re-affirmed that artificial birth control was wrong; i.e., deliberate frustration of the marital act is intrinsically evil and a sin against nature (exactly what PXI taught in Casti Connubi).
2) Relations during periods of natural sterility are not sinful in this respect (again reaffirming Castii Connubi)
3) Since couples may lawfully forego the marital rite (i.e., abstain from relations) for a grave reason, it follows that they may also observe the marital rite during periods of natural sterility for a grave reason
3.1) This is understood to be a decision made after prayer, spiritual counsel and possibly even dispensation; also it is not something one is compelled to do, rather it can merely be licit if certain conditions are met, and if certain conditions aren't met, it is gravefully sinful (though it is not the same sin described in castii connubi as there is no frustration of the act)
Here's a question for bowler, C101 or Allmonks: why is sterility not a diriment impediment to marriage? The Church does not forbid persons who cannot generate children from marriage, they only forbid those who cannot perform the act suitable for generation from marriage.
So, for C101 and Allmonks, perhaps the sede vacante began in 1917?