i) Sacramentalists believe there's something special about the communion elements that makes them a means of grace. The communion elements become Jesus. Or Jesus is physically present in the communion elements.
By parity of logic, what makes the baptismal water efficacious is that it becomes the Holy Spirit. Or the Holy Spirit is somehow "in" the water (like an eye-drop of dye dispersed in water). But sacramentarians don't argue for the nature of the baptismal water in the same way they argue for the nature of the communion elements. Why the lack of consistent explanation?
If the "presence" or identity of Jesus with the bread and wine is what makes it efficacious, doesn't that require a parallel in the case of water baptism?
ii) There's another problem with the sacramentalist inference. Because the Bible ascribes certain effects to communion and (especially) baptism, sacramentalists infer that there's an intrinsic link between the two, where the baptismal water or communion bread and/or communion wine causes a spiritual effect.
(This also depends on whether you think their prooftexts actually refer to baptism and communion.)
But let's take a couple of comparisons:
a) Samson's superhuman might is associated with his long, uncut hair (Judges 13:5; 16:17,22). But does that mean the narrator thought his hair was the actual source of his strength? Did he have magic hair?
But surely ancients Jews were aware of the fact that long hair didn't automatically confer superhuman strength on men. Indeed, not even Nazirites in general had superhuman strength.
So the hair wasn't what caused his superhuman strength. The hair was only emblematic. God assigned an arbitrary link between his hair and his strength. But his superhuman might came from direct divine empowerment.
b) Take the case of Uzzah, who was struck dead for touching the ark of the covenant (2 Sam 6:6-7). Is that because the ark was electrified? Like people who are electrocuted if they touch a live power line?
No, the ark was made of wood. The wood wasn't fatal on contact. You could use the same kind of wood to make many other harmless artifacts. It's not like death from eating a poisonous mushroom.
Rather, the ark was ritually sacrosanct object. It symbolized God's unapproachable holiness. It wasn't the ark that caused his death, but God.