A few points, easy to miss:
1) "Baptism" of desire is not a sacrament.
2) "Baptism" of desire means different things to different people, and as such, eludes definition.
3) The principle and necessary component for any "baptism" of desire to be effective is perfect contrition, for without perfect contrition, and in the absence of the Sacrament of Baptism, there can be no salvation.
4) If it were to be defined (and authoritative definitions are extremely rare these days!) "baptism" of desire would be framed in the context of a special case of perfect contrition, and therefore would be something that the recipient could lose ~ that is, one could have it one moment, and lose it the next, which is problematic for definitive authority to clarify. One never loses the mark of Sacramental Baptism.
5) The Sacrament of Baptism leaves an indelible mark on the soul that lasts for all eternity, but any "baptism of desire" would leave no such mark, and therefore calling it "baptism" of desire leads to misunderstanding, because it is not baptism, but merely a phrase popularly used to describe a desire FOR baptism.
6) There is no argument against desire, per se, among those who question the popular claim of "baptism" of desire. The problem isn't the use of the word, "desire," but rather the use of the word "baptism," because it isn't Baptism, at all. It is perfect contrition, which is a wonderful thing, something we ought to all strive to achieve at all times, but it is not a sacrament.
7) "Baptism" of desire is not dogma. It has never been defined, nor will it ever likely be defined, for the reasons above, and perhaps others. Therefore, questioning it cannot be a "heresy," and the subject is open to debate.