Regardie believed that self-initiation was valid. He believed that the LBRP, MPR, and Opening by Watchtower in particular, if performed daily for a period of months and years, would change the energetic level of the candidate, and invoke transformative and initiatory powers, sufficiently enough that they could consider themselves to be initiated, even into the Adeptus Minor grade. He believed that the Order in the 1930s was suffering from spiritual erosion, which seems to be an apt assessment from what we see of the history of the time, with documents being omitted, and high-ranking officers claiming grades they did not understand, let alone having the practical magickal skills to enact their mysteries and fulfill their gradework. It fell to the individual student then to ensure their own progress, and thus the whole notion of self-initiation came into play.
The problem with the sudent ensuring their own progress is manifold. It requires firstly that they be of a dedicated sort, that they practice the work (and not become an armchair magician, as so many do, increasing their book knowledge and their bookshelf at the expense of their spiritual knowledge and their practical magickal skill), and that they be determined enough to see it through. Having a lodge or temple, with various officers, helps keep people active, and a good officer can often whip a languishing student back into shape, saving them from their own erosion. The student must also have a strong discriminating mind, the ability to distinguish between illusion and reality, between deceptive entities and helpful spirit, and they need to have a subtle understanding of the multiple layers of ceremony, not to mention the oral tradition and "temple culture" that is often lost when one "goes it alone". They must also avoid rushing ahead, doing gradework beyond their grade, or falling pray to egotism, all of which can be avoided by a watchful Chief, who has (or, at least, should have) both the experience and know-how to spot and deal with these matters before they get out of hand.
The problem with self-initiation is that, because it's not presided over by a group of trained and qualified initiates (with at least one Adeptus Minor), there's no real guarantee that the initiation has been effective. For example, a candidate may undergo a Neophyte initiation at a physical temple, and they need not actively impart much to the ceremony. All they have to do is be receptive enough to let the energies impart upon their aura and affect their subconscious. All the real work is done by the Officers - the raising of energy, invocation of forces, assumption of God-forms, banishing, etc. When it comes to self-initiation, partcularly of the early grades where the candidate has little or no prior magickal experience, how can they compensate for the absence of these trained Officers; how can they ensure that all the appropriate energy is raised and assimilated, and the duties of all the Offices fulfilled? To do this has required a Probationer "grade" prior to the probationary grade of Neophyte, where the candidate effectively trains him or herself to the appropriate level to perform the ceremony properly and effectively. Tools are built, concepts or God-forms are meditated upon, and the ceremony is studied meticulosly.
However, the most important thing is this: these ceremonies are not to be performed once and then deemed to have been successful. Regardie was miffed at why people would perform a consecration ceremony and immediately consider themselves adept at such, without ever considering to repeat it at least one more time, if not dozens of times! Likewise for these initiation ceremonies. Indeed, there is far too much of beauty in them to be only experienced once, but the speeches and ceremony aside, the real purpose of performing these multiple times is to ensure that the full effect is achieved, that the initiation can be deemed true and proper, and that the entire ceremony can be considered effective and successful. If it is not, then you simply do it again. Indeed, considering how many mistakes we often make when learning new rituals like the LBRP, and how many more we make in the more elaborate ceremonies of the grade initiations, performing them multiple times is essential to simply doing them right. If you have the Kerux say the Heirophant's part, or you forget to circumambulate or knock, etc., then you are not doing the ceremony right, which may impact on how efficacious it is. With all things, practice makes perfect, and no student of magick worth their salt, however arrogant they may be, can consider themselves above this sage advice.
The problem with astral initiation is that you simply don't know if it was done, unless you are particularly sensitive to the astral world, perhaps becoming lucid in a dream where the initiation is taking place. Many people tend to "sell" astral initiations, and while they are definitely true and valid if actually done, the potential that they might not be lends me to be wary of them. I have participated in astral initiations, and they can be effective, but this was in a much closer and tight-knit community than what is often offered nowadays. Even if one does opt for this, I suggest they don't rest on their laurels and do nothing physically themselves. They should perform the ceremony even as the astral adepts are doing so. Physical enactment is one of the very tennets of Golden Dawn work.
The problem with physical initiation is that you need a temple, officers, and all those other resorces that go into forming a local group, because chances are (especially if you're in Europe) that there's none where you live. We can whine and complain at this lack, but at the end of the day it's the Work that matters, not a brick-and-mortar temple of brick-and-mortar brains. There is a lot of importance in physical intiation and temple work, and I hope to see more of it, but we should never dismiss self-initiation in order to bolster our numbers in our physical lodges, as so often is done nowadays, with people claiming all sorts of nonsensical stuff, such as being the "one and only authentic Golden Dawn", or claiming definitive lineage back to Mathers, which is just as difficult to prove as most lines of apostolic succession in Christianity. Lineage has its importance, but it's not the be-all-and-end-all, and it's not necessary. What is necessary is the Work, and your own personal dedication to fulfilling it. At the end of the day the true initiation comes from your Higher Self, as you are lifted up spiritually, and a piece of paper proclaiming an attained grade is only the physical manifestation of that internal process. As Above, So Below. If you have the paper and don't have the process, then it is meaningless, and you can consider the initiation to be rendered null and void. No one can confer enlightenment to another - we each have our own experience of Gnosis, an experience which makes us "more than human", and no mere human can decide on the validity of such.
If any of you have read my other blog, Henosis Decanus, you may have noticed my post on whether or not one could be self-ordained into the priesthood. In that post I highlighted how the priesthood is the equivalent of the Adeptus Minor grade of the Golden Dawn. There are also Minor Order grades (as part of Formation) prior to ordination that are the equivalent of the elemental grades of the Golden Dawn. In my post on self-ordination I highlighted some of the flaws of that idea, and I showed that it was not quite the same as self-initiation, though those flaws still exist with both. The issue here is whether or not you can self-initiate into Adeptus Minor and above. The differing views tend to narrow here and the usual answer is: no. The reasoning for this is that you need to be initiated in a Vault of the Adepti in order to consider that initiation valid and effective. Supposedly Mathers wrote a self-initiation ceremony for Adeptus Minor, however, so I guess the vote isn't really out on the matter. I will explore this particular issue in more depth in another post.