The Stewartsville baby is always stockpiled and available 100%, so I don't see why you wouldn't be able to do the same with a bloodroot baby if you go through all the effort to make it (the end result is providing an alternate to something that requires 0 effort or time to nab).
The quest to summon Mother Night has the lengthy Nai'Dorin Rite gating it, time-wise, and also the fact that it can only be done on the New Moon (the strongest gate of all, 1 hour out of every 32).
The nai'Dorin is not the quest that requires sacrifice. It is its own separate subquest that can be done on its own whenever people want to do it. The reward of the quest is, however, the time-sensitive component of the actual quest we're discussing (Summoning Night for a prophecy). (doing the nai'Dorin involves no harm to any young folk, just the Crow-standin who gets impaled on thorns and caressed with a fingerblade while he/she bleeds).
I just want to clarify this because I think it's important that we be accurate, I don't think the nai'Dorin itself is the issue at all here.
And I do still think that fixing the bloodroot baby quest to work as intended, and possibly adding a chamber in which to store it, would solve a good chunk of the concern without having to compromise any RP for anyone (since it does already exist).
As far as I'm concerned: Make sure that the blood-baby works. That's an already-existing alternative right there, there is an option to sacrifice a grown plant-"baby".
The entire point of the quest was another alternative (that takes a couple hours of grinding by killing Every Single Snake In The Game to do).
Glomdoring has been going heavily all-in on being friendly and welcoming to people, but at its core we're a forest where anything can and might happen. It might be dark, it might be unpleasant, but it's for the greater good of the Forest and all who live there. We're very definitely designed around being a Cult-ish organization.