Catholictrue, logic fails you.
What positive Catholic dogma would render BoD heretical? It's the dogma that the Sacrament of Baptism is necessary for salvation. Now, if one wanted to make some distinction while preserving this necessity of Baptism for salvation, one would avoid heresy, since one would not be directly contradicting the dogma that Baptism is necessary for salvation. Even if that opinion is false, the opinion would not be heretical in the strict sense of the word and could not be assigned the theoloogical note of "heresy". That's THE error of MHFM, the theological note they assign to the error of BoD (taken in isolation). Now, certainly, the vast majority (well over 99%) of BoD promoters at the same time embrace one or another actual heresies (such as Pelagianism), but BoD, taken in isolation, provided that whatever distinction a theologian makes preserves the necessity of Baptism for salvation (i.e. that salvation cannot happen without it), would not strictly be heretical.