So I find from time to time a moderate degree of anti-Reconstructionist sentiment among the wider Pagan community, and paradoxically sometimes from those who claim to be Reconstructionist's themselves. There are a number of reasons why people dislike Recons:
1. Reconstructionists are elitists.
2. Reconstructionists do not care about practicing a living religion.
3. Reconstructionism is no more authentic than any other form of Paganism
4. Reconstructionism is a waste of time because ancient religion has no value in the 21st century.
I shall address each reason below, but they all feed into one another to some degree, perhaps why they continually crop up among those who are opposed to the idea of Reconstructionism.
1. Reconstructionists are elitists: This is more of a sentiment, than an argument, but it permeates most of the arguments and really amounts to no more than an ad hominim attack, but a common one. Reconstructionists are elitist because they dismiss the opinions of other people and think their opinions are better then everyone else. This is a bit of a misnomer, because there is a difference between the weight of say a scholars opinion on a subject they have researched thoroughly vs. someone who has read a book on the subject but little else. I have no problem believing that someone who has spent the time researching something has a more informed opinion than one who has not. As such, because Recon's tend to be better read and eminently knowledgeable on the cultures they are reconstructing from, this can come across as being "elitist" because they know what they are talking about, and do not simply accept the claims made by someone who has not done the research.
2. Reconstructionists do not care about practicing a living religion: This criticism has to do with the "presence" of Recons, and the kind of discussions they tend to be involved in. Often involving academic topics of considerably specificity and minutia, often on understanding of cosmology, framework and mythology. As such topics like the practice of the rituals or an application of the understanding of cosmology is left for more private or personal conversations, and so the perception is that Recon's are only concerned with the scholarship, and not the application of religion.
3. Reconstructionism is no more authentic than any other form of Paganism: This is a bit trickier, as it needs to be clarified as to what "authentic" means. I would certainly say Reconstructionism is closer to the beliefs of [pre-Christian culture], than other forms of Paganism. The entire basis of Reconstructionism is the study of archeology, folk belief, literature and history in order to try and as accurately as possible reconstruct the earlier beliefs of a given culture; many forms of Paganism have no such focus. When it is pointed out that "we [Recon's] can't really know anything for sure" or "you [Recon's] are just stating an opinion, and it is no better than mine", what is really being said is that the one making such accusations give no heed to scholarship, yet we should be treating their opinion as equal to that of someone who has spent a concerted amount of effort studying. I think this is preposterous. I have no problem with Pagans who have made the decision to not try and incorporate historic elements into their practices; or have even developed a religion based on more modern discourse (such as many of the forms of neo-Druidism, largely derived from Victorian and early 20th century scholarship). The problem arises when one then argues that such a belief is (despite its modernity) the same as it was in [pre-Christian culture], when it is clearly not the case. Not everyone who denounces Reconstructionism necessarily does this, but it is disconcerting how frequently this particular claim is made especially in the guise of "The [pre-Christian culture] made it up as they went along, so why can't I?", the answer of course is that you'd first have to prove that "they were just making it up", which is simply not the case when one has actually studied [pre-Christian culture]
4. Reconstructionism is a waste of time because an ancient religion has no value in the 21st century. This is becoming a more frequent claim, as many sensible Pagans realize the fallacious nature of argument 3. Unfortunately this criticism has its own problematic issues. The chief concern I have is if ancient religion (and the deities they worshiped) have no value, or no applicability to the modern Pagan, why bother with the worship of those deities at all? I have yet to see a compelling response to this question. I believe that if one is going to worship a pre-Christian deity, then they ought to learn as much about the culture that knowledge of said deity was developed in. This gets back to fundamental issues of cosmology, and how one see's and understands the cosmos; as in any scholarly, effort context is of vital importance. Understanding the cultural context in which worship of a deity occurred historically, provides the best means of trying to understand said deity within the larger cultural framework in which it was originally understood. This is doubly important for GRP's because the mythic texts we have are all Christianized to some extent; understanding what is [supportably] pre-Christian then is dependent on one's knowledge of the pre-Christian culture of the Gaels and corresponding cultures which share cultural and linguistic roots. Without this knowledge, one is going to come away from the myths with a very different picture of pre-Christian deity, which will unfortunately be wrong.
There is certainly room for innovation, there are certainly aspects of pre-Christian culture which is so wholly divorced from the modern, that recreating it would be difficult, to say nothing of he wisdom of doing so. This often comes with accusations of "selective arguing"; based primarily on an "all or nothing" gambit. Why is it okay for you [Recon] to pick and choose what elements to recreate, but not okay for me [eclectic] to do the same? I would argue that this is decidedly a wrongheaded approach. As far as I have experienced Reconstructionism, the central component is found in recreating and adopting the world view of [pre-Christian culture], everything else follows from this. So for example, many have commented that [pre-Christian culture] performed human or animal sacrifices, had slaves, engaged in blood feuds, had trial by ordeal, and so on. The argument then becomes for Recon's to have any meaningful claim to authenticity, they need to do these things as well, or the whole effort is moot. However, with an understanding of the why behind such beliefs as the necessity of sacrifices, or the context in which blood feuds arose, provides a good reason as to why these elements need not be recreated (or could be adapted) to suit modern sensibilities.