Welllll.. lets get this thing straight - some branches of christianity are in fact prohibit you from reading that stuff. Only priest shall do it.

Secondly, lets not go in that argument at all. Back in days of serious orthodox church it was considered as dirty to eat/speak/live with catholics. People were told to throw away plates&silverware if they had to have catholics in their house as guests. Few centuries after in totally different part of the civilized world, namely England, people were keeping warm in winter by burning catholics.

So lets not go in depths of living by the word of the God, as christians could not sort things amongst themselves, though they presumably going after same things.

As of whole marriage thing - as correctly was pointed out - it did exist LONG before Christianity ever started, and will probably exist in some form long after it will be forgotten (unless humankind will manage to curl up and die of course. Which is somewhat possible given the current pace of things)