Be honest - when's the last time a Christian pushed his beliefs in your face?
An advert on a bus for a course could be akin to an advert for a type of stamp (for example).
The example may not work but the point stands - he has too much personal hatred/dislike of Christianity (especially) to be taken serious as a Scientist. The man has no open mind, and uses science to push his view on to others - much like how people twist the words of the Bible/Torah/Guru granth sahib/Quran to their own agenda.