Unless the rules of the Puritan Board are changed so as to disallow adherents to the 1689 LBCF, the catagorizing of "Baptists" as "heretics" (along with the Anabaptists of the 16th century) would be a contemptible libel, not an accurate label. Remember that when the Presbyterians were racing all the other lemmings jumping off the cliff to become unitarians in the 18th century, it was those pesky Baptists who held to Calvinism.
I know this is sort of "technical" but it sort of goes to the problem of labels. I wasn't certain how useful this discussion was when it came up.
The exact rule is that we're not supposed to call another man to repent of a sin if he is holding to his Confession on this board.
It sort of goes without saying that adherence to a particular Confession implies that another Confession is in error about the nature of the Sacraments.
The real question here is whether that error is properly labelled heresy or not. If it is then the discussion cuts both ways. In other words, if the label sticks then it is appropriate for an LBCF adherent to label the Sacraments as heresy (and some clearly do).
I don't necessarily have a problem with the discussion but we do still have a rule that we'll be bogging down the discussion with a "You need to repent of your heresy..." tit for tat. It might seem like a silly thing to allow for us to allow people to come to the conclusion that a particular activity is heresy but to not allow them to actually apply the label to a particular individual but I think there's a difference between defining error on the one hand and the work of the Church courts to convict of an error on the other and there is a difference.
I've made my opposition to the credo understanding of Baptism very plain in other threads. I think, as an ordinance of the Church, it undermines the nature of the Gospel by centralizing the ordinances in the will of man. But I also recognize that the Baptist is doing so because they believe it is a logical conclusion from their understanding that God only Covenants with the Elect. On the one hand, the Reformed Baptist fully affirms that the benefits of union with Christ flow only to the Elect just as the Presbyterian. On the other hand, I believe they err severely in their understanding of the Covenant of Grace and how God has visibly manifested His plan of redemption in time and space and announces His promise to His people and provides Word and Sacrament for the conversion and building up of His Elect toward His Holy ends.
I don't think I would call the Reformed Baptist practice heresy because they retain the understanding of Christ's atoning sacrifice and that God only blesses the Elect with the benefits that union with Christ confer on the basis of faith alone. I would call their visible ordinances error and continue to try to remind them that they're not achieving the goal they believe by disobeying God in how He has ordained the visible administration of His Covenant.
On the other hand, if re-baptism is on the basis of a soteriology that is no Gospel at all then that is a different matter altogether. In my mind, it's not the act that's nearly as important as what the persons performing the act think they're about. I have no problem calling the Anabaptists, and others like them, heretics.