The idea is to make fish appear as cute and cuddly as kittens, so that people feel sorry for them and feel uncomfortable when thinking about slaughtering or eating them.

To a certain degree, I do agree with that - just because fish don't scream doesn't mean they're not in pain. If we anyone killed cows, pigs and hens the same way fish are being killed, say by drowning or suffocating them, it would be a big scandal.