The critic of the author may be correct that there is no reference to Marco Polo saying that quote, but if you look at the following book he wrote and search for "cut" you will see the many times the act of chopping off heads are mentioned. So the quote may be wrongly contributed, but the description of what was implied is clearly there.
http://www.gutenberg.org/cache/epub/12410/pg12410-images.html
The real issue is should a person not be allowed to make statements about Islam that are factual? Should it subject the author with great penalties if they do?
Remember the history of the tragic abuses of the Greek people and nation by Turkey, they were at one point literally thrown into the sea.
Looks like an attempt to establish precedent of sharia law in the international court system.
If I woke up tomorrow and learned that every snake infested islam pit (mosque) had burned to the ground in America, I would first smile and then reload for the pissant islams that will reek from the woodwork.