The Ordinary Form has been blessed by the Holy See and is not considered heresy.
The problem there is that the “ordinary” form in the US is not the “Ordinary Form,” but an admixture of local innovations, several things permitted only by indult (e.g., communion by hand), and a particular translation that
has been declared invalid and heretical by Cardinal Arinze in
Liturgiam Authenticam.
I take issue with any “traditionalist” who tries to say that the
Latin translation of the New Mass is “heretical”. Granted, there are serious theological questions regarding Eucharistic Prayers II-IV, but those can at least be chalked up to the Church’s power to “loose and bind.”
If you look at the Novus Ordo in Latin (with Eucharistic Prayer 1) and compare it to the Traditional Latin Mass, there really isn’t much difference: mostly just the stripping away of a lot of beautiful poetry and a lot of redudancy from the Extraordinary Form. This is why Benedict calls them “forms”: they’re essentially the same liturgy with just a different artistic expression.
However, if you compare the Latin text of the New Mass to the current English text, there are
far more significant differences in meaning than between the two versions of the Latin Mass.
My problem with increased use of the TLM/EF is that expressed by Cardinal Arinze: if people go to the TLM, they will be less inclined to fight for the “Reform of the Reform”. Right now, most of the relatively few parishes that have the New Mass in Latin (e.g., the way EWTN used to do it; what trads call, inaccurately, the “hybrid Mass”) because they don’t have access to the TLM.