There is nothing wrong with citing Jung on alchemy, nor in even using his texts as a foundation for understanding spiritual alchemy. Most discussions of late, when not coming from Fr. AIT and his lot, center on spiritual alchemy. And there is nothing wrong with that.
I become dismayed, however, when the Alchemical Stages (e.g. Nigredo, etc.) are used to validate the subject of Gnosis. This conflates the spiritual technology of the Gnostic sects (such as displayed in the texts belonging to the Nag Hammadi library) with the literature of the alchemy, which is actually older in some situations. There may be similarities between the two subjects, but suggesting they are one and the same is just... unthinkable to me.
Gnosis - divine knowledge - is exactly what it sounds like. Some aspects of it may well depend on a contingent state of the soul, but some are simply available to everyone, from the moment they set out on a spiritual quest to free themselves of the Archons. Or whatever.
Seriously, though, we could also have some folks stop endlessly conflating Lab Alchemy with Spiritual Alchemy. The former requires decidedly more resources, and seems to have some crazy perks to it. Whenever I end up with the money to seriously pursue it, I intend to. And yes, I know that Bartlett explains how to perform a number of alchemical operations cheaply. I still want a damn spagyry set before I set out to bring forth the virtue in plant matter and evolve it.