i'm a christian and i think that what this pilot did was rather unprofessional.there's a time and a place for everything,and the cockpit is not a place to preach from! this sort of thing really doesn't give a very good image of professionalism to the pax at all.
Sadly,as always,there are those who bring islam into this (i suspect mainly because of a deep sense of suspicion/envy/fear/resentment of muslims).the fact is that outward displays of religious practice are very much a part of their culture,which is foreign to us westerners.Thats why,when you hear a prayer on Saudia or whatever,It is perfectly normal to the majority of those on board.
Conversely,such outward manifestations of Christianity are not the norm in the West,so its obvious that such 'preaching' constitutes something that DOES NOT FORM PART OF OUR CULTURE.This is at the heart of why what this pilot said is not professional,proper or desirable for the image of the Airline.
As a christian i see my religion (which incase all those muslim-haters don't realise,is practised DIFFERENTLY to islam,which is a much more publicly practised,homogenously observed religion) as a deeply personal thing,and i can understand why this guy's preaching made people uneasy.