I feel like that confuses the issue and makes it easier to argue against - humans are very clearly different to dolphins and equating the two does noone any favours.
This is very simply an extension of the Golden Rule to other sentient species beyond humans, starting with the ones that we know about and are closest to us.
And as Colin points out, the "equating X to humans does no one any favours" line has been used before in history.
"These savages are clearly different
from civilised people"
"... and equating the two does no one any favours."
In the same way, some people put dolphins in captivity, and consider it an inconvenient side-effect of tuna fishing that dolphins are regularly killed in large numbers. And yes, some people eat dolphins, and that supports an industry that kills them for profit, just as slave traders used to capture people and ferry them across oceans. For profit. Deaths of a percentage were considered acceptable losses.
It seems to me that the parallels are stronger than the differences, and I also wonder how people of the future will judge the actions of today, and silence of those who didn't speak up.