Interestingly, in Evangelium vitae, John Paul II himself uses the phrase responsali paternitatis ac maternitatis, so he himself must sense the incompleteness of conscia, especially since Gaudium et spes speaks three times about "responsibility" in the section on marriage and family (47-51).
Also interesting, EV uses the phrase paternitatis ac maternitatis, rather than simply paternitas, like HV. This echoes GS's Coniuges autem, dignitate ac munere paternitatis et maternitatis ornati, officium educationis praesertim religiosae, quod ad ipsos imprimis spectat, diligenter adimplebunt. "Graced with the dignity and office of fatherhood and motherhood, parents will energetically acquit themselves of a duty which devolves primarily on them, namely education and especially religious education." John Paul II is reminding us that the office of fatherhood and the office of motherhood are not interchangeable. HV doesn't mention motherhood at all, interestingly.
On a final note, until I found it in EV, I've never until now made the connection between "Mater" and "materia." Matter and Mother. "Moreover, once all reference to God has been removed, it is not surprising that the meaning of everything else becomes profoundly distorted. Nature itself, from being "mater" (mother), is now reduced to being "matter", and is subjected to every kind of manipulation" (EV 22). Hm.
Origin of MATTER
Middle English matere, from Anglo-French, from Latinmateria matter, physical substance, from mater