Is believing you are doing the will of God (i.e., the Church) sufficient?  Doesn't Christ answer this question when he says, "They will put you out of the ѕуηαgσgυєs: yea, the hour cometh, that whosoever killeth you, will think that he doth a service to God. And these things will they do to you; because they have not known the Father, nor me."  (John 16:2-3).  And just prior to this statement, He tells you that he is saying this so you won't be scandalized.

I have often told people just what these folks say above.  

That's really weird. Br. Peter has a whole debate where against Albrecht where he debunks that "This is my body" is enough for validity. MHFM always attacks the form, first time I heard anything about the intention from them. Is this something old?

This is from the e section of his website. It's very recent.

Each consecration stands alone. They are not tied together in terms of validity of the consecration of the species itself. However, a valid Double Consecration is necessary for the Holy Sacrifice to be properly consummated, because the Double Consecration represents (Sacramentally) the separation of Jesus's Body and Blood on Calvary. 

If you read De defectibus, you will see examples where one consecration of the species can be valid when the other consecration is not. In those cases, De defectibus requires the minister to re-consecrate the defective species, but not the other one.

The Novus Ordo "consecration of the wine" is invalid per se because "the form" omits the words "mysterium fidei" from words spoken at the point of "consecration." Yes, the words, mysterium fidei are found in the text of the Novus Ordo missal, but they are explicitly NOT part of the consecratory words, as those words are defined by the General Instruction of the Roman Missal (GIRM). 

According to the GIRM, the "consecration of the wine" ends with the words spoken BEFORE the priest genuflects. The words "mysterium fidei" in the Novus Ordo are said by the priest AFTER that genuflection, so those words are not part of the consecratory formula in the Novus Ordo. This contradicts St. Pius V in De defectibus, which was promulgated infallibly by the Papal Bull Quo Primum.

The Novus Ordo "form for the  "consecration of the host" is not necessarily invalid but can be invalid because of lack of valid intention, matter, or minister. The problem of invalid intention comes up because the words of "the form" (this is my body) are normally said in a narrative style. And so, for example, if the priest thinks that he is just recounting an historical narrative (and not instantiating Christ's Body), then his intention causes the invalidity in that species.

Even if the "consecration of the host" is valid in a particular the Novus Ordo liturgy, this does not make it good. In fact, the scenario where one consecration occurs without the other is called "nefas" (wicked, evil) in 1917 canon 817 (and 1983 canon 927). So, either way, the Novus Ordo is sacrilegious. In no sense, can it properly consummate the Holy Sacrifice because "the form" of the consecration of the wine is always defective by omitting "mysterium fidei."