Here we see the cultural difference among countries...
Here in Italy everyone is OBLIGED to help endangered people at the best of his/her capabilities, whatever their certification. Going away and avoiding to give help is a severe crime, which is prosecuted by the public attorney. And this without anyone suing anyone else. If found guilty of help omission, one goes into jail for some years, in case the missed help caused the death of someone.
So here it is legally quite risky NOT to give help...
Of course this is not only for scuba diving, it is also for swimmers, cliffhangers, skiers, on the road, in any public or private site.
When young, I was certified as a professional caregiver both for swimming pools and in the sea. Of course this certification lasts only one year, and must be renowned every year after a thorough medical visit, as it allows to work in the surveillance staff. Every 5 years you have to repeat the exam, so I gave up. But it was required for becoming diving instructor.
I also did apply in the civil protection as a volunteer, but in this case not for providing help to people still alive, but as an expert in recovery of dead bodies (mostly in muddy waters of rivers) . After doing this for a couple of years, and after one successful body recovery, I did get the acceptance for doing my military service as a firefighter, instead of as a normal soldier.
During that year as firefighter I made dozens of live actions, also including savage of endangered people, a couple of times.
So please understand my point of view: who turns away from a danger situation where there is people risking their life, when he could provide useful help, is a coward and an human excrement!
The risk of being sued appears of little relevance to me, it is just a civil action, it is just money, in the end.
But how could I sleep again, knowing that someone has lost his or her life, and I could have saved them and turned away? How this can even be suggested, here on Scubaboard? Who is giving such advice should be prosecuted too! And here we have also that type of crime, it is called "apologia di reato" (crime apology), up to three years in jail...