It is not something I would do outside of a private course frame, but I can understand why some others would, though I don’t always agree with the reasoning. In some cases, it is a joke. In some cases, the authors have co opted the convenient aspects of Vodun and put it in a western frame. In some cases, they are workings that are common for laypersons and aspiring mystics to do for themselves, and only called spells because the term “working” isn’t as well understood. In a few cases though, it is that a mystic and author wants people to know what is involved in doing a working, so that they appreciate the cost and effort of their priest.
So long as they are posted in the context of educating people, and spiritual and psychological readiness is taken seriously, it is not something I personally view as wrong. The problem is that readiness is seldom approached because the author either takes for granted that anyone doing the working would be a consistent practitioner who is at least doing regular offerings to Eshu, or they are overly westernized and don’t consider it important.
Take amarres, for instance. Most people who would search for how to do an amarre would be practicing Santeros or somewhere else in the spectrum. They are wearing or carrying amulets, and do weekly offerings to Eshu and whoever is their head, if it is known. So they would be ready to do a normal amarre. Because they live in awareness, it would also have a better chance of working.
If they are not practicing consistently and giving regular offerings, because of a lack of time or because they are mystically aware, but not so mystically inclined, they would read the instructions and easily understand to put this in the hands of a priest. So knowing how it is done lets them know that they are not equipped or should not try to do it themselves. No harm is done.
However, for some people, posting the instructions leads them to believe that they can jump in without any preparation or protection. Even worse, most of the instructions I’ve seen online do not begin with offerings and asking the permission of Eshu. Without asking Eshu, all of whatever efforts and expenses people go through to do Vodun and diaspora like “spells” are wasted.
This is not to say that all spells anywhere must start explicitly with the name Eshu or Elegua. People who are not Eshu aware may still have the equivalent in their belief system. In some faiths, there is another similar Spirit or a kind of abbreviated word to open prayers. What I’m saying is that something must always be done to approach the Spirits with the right mind, and in Vodun, this is the call to Eshu.
So if you come across a “Voodoo spell” that does not begin with calling Eshu, it is not going to work and probably posted by someone who knows nothing of Vodun. If it does, then they are likely posting it with good intentions for the sake of educating the public and increasing appreciation of the work of priests.