I think you are totally overreacting. But I can sort of see your perspective.
For everyone saying that all state schools should be secular - you DO remember that we don't have a separation of church and state in this country? And that our monarch is the Head of the Church of England...right?
So even if in practise we are actually much more secular than other countries who DO have a separation between the two, but only really in theory (USA anyone?), C of E is still the State religion. Therefore, it makes sense that some schools only have C of E people coming in.
It's not a personal attack on people of other religions. It's logical that as the religion of the State, it is reflected - MINIMALLY - in schools.
Getting in a flap over "indoctrination" from a once weekly visit is ludicrous. If you have genuine concerns that the person visiting might be using the visit inappropriately (eg saying all gays should burn in hell, or that C of E is the one TRUE religion and everyone else is evil), then that's one thing. But if it's just a guy coming in, talking about his community work, or giving a service (that no-one will be paying attention to anyway), then....well you would sound pretty hysterical.
If it helps at all, I went to a faith school for years and years and YEARS. Our Religious Studies were focused entirely on Christianity (but from a practical and historical point of view, like the differences in translations, why some gospels were considered ok and some excluded from the bible, political situation with the romans and judaism at the time...that sort of thing).
We had religious assembly every single day and sang hymns. We had mass multiple times throughout the term. We would have talks from people in the Christian community, and the vast majority of our teachers were involved in work within the community as well.
I would say that about 85% of the people in my year grew up to be agnostic, atheist, or not giving any religion any thought at all. The remaining 15% were people who had very religious parents to begin with.
So try and have a bit less hysteria, and a little more faith that a person's brain isn't so pathetic that it can be indoctrinated so easily