@mahtan
Throughout history, there are many instances of problems which were easily resolved (say hand sanitation before handling babies to greatly decrease child mortality) because we didn't know any better. There are also plenty of rituals which have no grounds on reality but which were still done because they were harmless or didn't harm the society enough to be a problem.
Of course, the consuming does not need to be a problem, but Myne happened to live in a place and time when a commoner with the Consuming is most likely to die from it as a young child while their family would only be able to think that their child happened to be too weak (unknown reasons for child mortality). Nobility, who have mana, live completely segregated from commoners and if they do not need new blood they do not particularly seek to find and integrate commoners with mana and split their wealth and power (they're already sometimes in situations where they send some of their children to manage the churches). After all, the original nobles must have learned to use their mana on their own, just as Myne used her mana when she attacked the head priest, so it also makes sense to only look out for that.
Also, the use of toronbe hardly seems convenient. If there's a baby suffering from the consuming, you'll just bring a toronbe to touch the baby with, then throw the toronbe, and start hacking? The alternative to having tools that such out mana is for the person to forcefully use their mana and spread it (say in the ground), but when there's no such thing as school for commoners, who will even be there to teach those exceedingly rare cases of commoners with excess mana?
So yeah, personally, I don't have an issue with the consuming currently being a problem.