The answer is C: The cannibals
There are some references indicating that Crusoe is most likely describing the cannibals. For instance, 'The people from that country' being separated or distant from civilization ('disposition of the world'), without influence of moral and law, resort to 'horrid things', guided by 'their own abominable and vitiated passions.' and receiving 'such dreadful customs.'
To vitiate: to destroy or damage something
Dreadful: causing fear, shock, or suffering