HareBrain
You are correct about the idiots hassling whales etc. A lot of this is education. And the way the diver operators run their business. However, it is also sometimes problematic how important such controls are.
I have snorkelled with a whale shark. Off Exmouth in Western Australia. I had about 20 minutes almost alone with it, because all the other snorkellers were fat and unfit and got exhausted. The whale shark does not stop swimming and you have to swim to keep up, while quickly eliminates the unfit. The operators laid down the rules before anyone got in the water, and they had a dive guide in the water as well to ensure everyone behaved.
I have snorkelled with dwarf Mincke Whales off Cairns in Queensland, Australia. Very tightly controlled by the operators. We all had to stay on the surface and hold onto ropes. I suspect the real reason was not to avoid hassling the whales, but to keep the divers close to the boat where they could be watched. I often wonder how important those controls are, from the whale viewpoint.
I have also snorkelled with a dwarf Mincke whale in South Minerva Reef with no controls at all. About 10 divers snorkelling with it, and the whale seemed to enjoy every minute of it, following us around.
Here in New Zealand, I have snorkelled with three species of dolphin (and a fourth in PNG), and with fur seals. There is no indication that they were at all stressed. It is a big, big ocean, and they can swim away from divers if they wish.
The humpback whales in Tonga do not seem to be hassled, since they are becoming more and more friendly. I think they have learned that the divers will not harm them or their calves. I think that this outcome is way cool!