As things change in the dive industry, so too should this attitude. It is outdated, and has no place in modern thinking. If you are a captain of a charter boat, the Coast Guard WILL hold you directly responsible for the lives of your passengers, whether they are on or off the boat when they get hurt. Your insurance company (you do have in-water liability for your charter boat, eh?) feels the same way. Willis Canada has been dropping charter boats from insurance for defending their actions by saying "I'm just the transportation to the dive site".
I assure you that you will lose your license when you flip that attitude to the investigator when he comes to investigate a fatality or serious injury on your vessel. It used to be that Coast Guard investigators were relatively stupid when it came to sport diving accidents. I assure you that the ones in Galveston, Panama City, and Key West are not stupid or inexperienced when it comes to sport diving accidents. They know the regs, they know how to dive, and they don't take attitude from charter boat captains. Imaging my surprise at my last investigation.....