Regarding the historicity of Pagan traditions. Given that we know next to nothing about what ancient druids (if they were really as described by the Romans) got up to or believed, or what medieval witches (who, even if they existed, were probably not pagans) got up to, or what early medieval heathens got up to (a bit more data, but a lot of it written down by Christians), the people who claim that they're doing something because their ancient forerunners did it, and not because they feel it to be the right way for them to be a Druid/Witch/Wiccan/Heathen/Pagan in the here and now - that is what is irritating to the academically-minded.
You can be a Druid/Witch/Wiccan/Heathen/Pagan because you feel you are one because it fits the image you have in your mind of what a Druid/Witch/Wiccan/Heathen/Pagan is (and I affirm your right to do so).
But what happens when someone else with a completely different idea about what a Druid/Witch/Wiccan/Heathen/Pagan is, does the same? Then we have confusion...
What is the solution to this dilemma? I'm not sure that I know. I know that we do need to have discussions about our theology, our values, our worldview, our ethics, and what is distinctly Druid/Witch/Wiccan/Heathen/Pagan about them. We don't want to establish a creed or an orthodoxy, because that could lead to persecution of dissenters. But that does not mean we can dodge the issue and just not talk about it.
As far as historicity is concerned, the rest of us could learn a lot from Heathens and reconstructionists, who have gone to the effort of reading as much of the available source material as possible, and comparing it with experiences and ideas of present-day Heathens, and creating a synthesis of historical and present-day insights. They are lucky because early medieval heathenry lasted a lot longer and was better-documented than other traditions. They also have a well-worked-out and widely publicised set of Heathen virtues. Wicca also has a set of virtues, but this is not so well-known.
Personally, I feel that we are also the heirs of the Renaissance, Reformation, Enlightenment, and Romanticism, and we cannot just ignore the intervening centuries and pretend they didn't happen. This is one of the reasons why I am interested in Unitarianism.