Mith,
Answer the question - How is it that a heretic can possibly have the proper intentions?

In case of necessity, as long as the heretic, Jew, Hindu, infidel, Prot, etc. says the words and pours the water, the baptism is valid because that is what the Church *does*. Trent says "with the intention of doing what the Church doth" not doing what the Church intends, or with the correct intention.

It is the act of doing what the Church *does* that Trent speaks of. If the heretic is expected to have the proper intentions, then explain how that would be possible.

Quote from: Trent's Catechism

Ministers In Case Of Necessity

Those who may administer Baptism in case of necessity, but without its solemn ceremonies, hold the last place; and in this class are included all, even the laity, men and women, to whatever sect they may belong. This office extends in case of necessity, even to Jews, infidels and heretics, provided, however, they intend to do what the Catholic Church does in that act of her ministry. These things were established by many decrees of the ancient Fathers and Councils; and the holy Council of Trent denounces anathema against those who dare to say, that Baptism, even when administered by heretics, in the name of the Father, and of the Son, and of the Holy Ghost, with the intention of doing what the Church does, is not true Baptism.
And here indeed let us admire the supreme goodness and wisdom of our Lord. Seeing the necessity of this Sacrament for all, He not only instituted water, than which nothing can be more common, as its matter, but also placed its administration within the power of all. In its administration, however, as we have already observed, all are not allowed to use the solemn ceremonies; not that rites and ceremonies are of higher dignity, but because they are less necessary than the Sacrament.

I know, Stubborn.  The intention of doing what the Church DOES is precisely the matter at hand.  The Church performs a rite instituted by Christ when it baptizes.   Do heretics always and presumably intend to do that?  If they did, the Church would not have a practice of conditionally baptizing converts.  

For ministers who view the sacrament as a mere public initiation into the Christian community, it can be difficult to determine whether or not they actually have the proper intention.  If they do not believe baptism is a sacrament it can likewise cloud the issue in doubt.  A doubtful sacrament cannot be treated as if it were valid; the issue here is not valid vs. invalid but also takes into mind that there may be doubt, in which case it is considered invalid and treated as such, hence "conditional" versus "absolute" baptism.