I would explain to the client that they hired you for your expertise and part of that includes how the images are processed. Being such, you do not feel that it is their best interest to have access to the RAW files since they would not be able to process them to your level of quality. Furthermore, it does you no good to have RAW files available for the public to see that have not been edited to your standards. Having image such as this out there for people to see could have a detrimental effect on your business and tarnish your reputation.
If they do not buy this, revert back to the contract which states they only get 5 images and refuse to hand over the RAWs.