Apparently subtle distinction.
There is a difference between learning about a subject, such as Islam, and proseltizing, that is, promoting it.
Many people learn about communism, for instance, in economics classes without any attempt to turn them into card-carrying communists.
The Christian activities which are protested are the practice of Christianity, not the learning about Christianity. What happens when church and state are mixed is extremely unpleasant. The Spanish Inquisition came about, governments such as Iran, AGs like Ashcroft.
Too subtle a distinction for conservatives, apparently. Liberals tend to not be afraid of learning about others beliefs.
Arf