"Maybe at the solstice the church would like to open its doors so we can help celebrate this celestial event in the way we wish in their sacred space."
The gods know that I'm no Christian, and no lover of Christianity. But these days I'm very wary of getting all us-and-them with Christianity. Better to simply try to ignore them than to honour them with enmity. Don't give them the airspace!
I'd object to their ceremony because it was making a whole load of noise and therefore inflicting their trip onto everyone present at Avebury, not because Christianity was intruding on a "pagan" space. If they had been a bit quieter about it I wouldn't have a problem - hell, being at the stones might even do them some good, eh? I feel the same way about certain new-agers/druids/wiccans I've encountered at stone circles, with their clanging gongs/beating drums/chanting/messy offerings. I also feel the same way about English Heritage forcing their horrific capitalist trip onto everyone at Stonehenge. Or the BBC inflicting their trip onto everyone when I visited Callanish. Or the camera-wielding tourists inflicting their trip onto everyone at so many ancient sites. So yes, those Christians were out of order, but not because they were Christians, but because they were dominators (as some neo-pagans, tourists, TV programme makers and many others also are).
Even if Christians didn't occasionally get up to this kind of thing, its true that many different kinds of people visit the stones for many different reasons. I don't respect all of those reasons, but I feel strongly that the stones are for ALL, not just for those who call themselves pagan, or those who call themselves tourists. Being a Christian doesn't mean you shouldn't be in a stone circle, just as being a neo-pagan (not that I'm implying you definitely are, although it sounds like you might be) doesn't give you more right than anyone else to be there. Tolerance and respect are what it's all about, and that means putting up with ideologies that you don't share. The Christians you mention were wrong to do what they were doing because the way in which it was done lacked respect for others who were present. We shouldn't become intolerant about their religion because of it, though, they are entitled to believe in whatever they like, however misguided or messed-up.
I say these things because I detect more than a little intolerance in what you say. You make it sound as though a brass band would be completely acceptable if it were part of a neo-pagan handfasting thingy, for a start. You also seem strangely prejudiced against old ladies? You say you don't care what people choose to believe but the rest of your post shows that you don't really think that. Elsewhere, for example, you say "not only is it crossing a boundary too far but the fact that the service was amplified meant it was in-escapable", thus implying that Christians should not be welcome at Avebury even when they leave their amplification at home.
A related thought: are today's pagans part of the same tradition as that which resulted in Avebury's construction? Can the twenty-first century people who attend Stonehenge on the morning of the summer solstice be said to be a part of the same tradition as those who attended it at that time of year in Pre-Roman times? I tend to think not, but since I can't decide for sure I reserve the right to change my mind (as I always do, I suppose, even when I feel certain!).
