Whales are much closer to being extinct than most any other domesticated animal. They also don't reproduce at the same rate. The argument not necessarily that its individual life is inherently more valuable than say a cow. But to the rest of its species it is comparatively more valuable.

As a thought experiment, imagine someone killing the last member of a species. Then when you criticize them, they point out you ate chicken so you're both equal. You'd think them a moron. This is a lesser version of my example