Calculating the Harms

Thanks to Richard for his interesting response.  I guess I was wrong to assume the fourth factor was the easiest one.  Richard says:

Regarding evil effects: Even if we were to assume that there is no objective evil in avoiding pregnancy during intercourse as long as this effect is not subjectively intended (something which I doubt), there remains the complex but real evil of giving "scandal" both in the act of using a condom and in the teaching that this is permissible.

On the point of the lack of evil of avoiding pregnancy without subjectively intending it, I'm confused by Richard's doubts.  How would the contrary view (that this is in fact an evil) be reconciled with the Church's endorsement of the rhythm method (which is frequently touted in terms of its effectiveness at avoiding -- oops, I mean "spacing" -- pregnancies) and, perhaps more on point, the therapeutic use of oral contraceptives?

On the question of the other harms, I'm not sure I see the scandal of a new teaching here.  (In fact, in light of the permissibilty of the therapeutic use of oral contraceptives, I'm having trouble understanding a clarification in this area as a wholly "new" teaching.)  In any event, the context of married couples where one has HIV is pretty circumscribed.  Personally, I'm more scandalized by the thought that such a couple would be taught that it is prohibited to use a condom, knowing that they will likely have unprotected sex and transmit the HIV virus to the uninfected partner (usually the woman).

I suppose I agree with Richard that the DDE should include a requirement to use the least harmful means to achieve a good end, though I don't think that is a traditional element of the doctrine.  Michael Walzer, for one, has proposed it in his discussions of ius in bello, and it seems reasonable to me.

UPDATE:  In response to Michael's helpful post, I should clarify that this question only makes sense in the context of an assumption that Humanae Vitae is correct.  I, too, disagree with HV and only pose the question because it seems to me a very plausible use of the (much abused) doctrine of double effect, even for those who accept the traditional teaching.