Ah, but this DOES prove that the condition of "necessity" is not violated per se by an in voto reception of the Sacrament ... since Trent taught that Penance could be received in voto.
This is true. It is one of the reasons certain theologians, doctors and supporters of BOD may have come to a false position of BOD. It is somewhat deceptive when read in isolation. This is why I gave the supporting information Ladislaus. Trent, Session 14, Canon 2 has to be read in context with the rest of the Council. Just because necessity does not always mean "absolute" necessity, when Trent, Sess. 14, Chap. 2 is read along with the supporting data, it rules out Baptism of desire. It also shows that in comparing the necessity of the two sacraments for salvation, Trent was not referring to how the grace of each sacrament was received, but that the sacraments of Baptism and Penance were divine (not human) laws.
So it's NOT a heretical denial of the necessity of Baptism to say that Baptism can be received in voto.
If the Church says something concerning faith and/or morals is absolutely necessary to received, then it would be heresy to say it is necessary merely in desire (even if the word "necessity" is not always taken absolutely by the Church). Of course this heresy can be "material", if there is good reason for the person being deceived. Once you deny dogma, you are not merely in error anymore. For example a protestant may say "I believe true faith is necessary for salvation. Good works are also necessary for salvation (but not absolutely necessary). Even if one does evil, it is enough that one "desires" to do good works."
Now a protestant is a heretic for believing this, even if he tells you that the Church doesn't always regard "necessity" as being "absolute".