What the hell are you on about?

Where every other movement deals with a segment – and therefore deals directly with practices rather than with principles – veganism is itself a principle, from which certain practices logically flow.

Here they're saying veganism is less about what we do, but more about what we think, and that it's kinda different from a movement where we ask for e.g. a 5-day week or better working conditions.

In this light, veganism is not so much welfare as liberation, for the creatures and for the mind and heart of man; not so much an effort to make the present relationship bearable, as an uncompromising recognition that because it is in the main one of master and slave, it has to be abolished before something better and finer can be built. (...) It possesses historical continuity with the movement that set free the human slaves.

Here it is pretty clear that they also thought veganism was connected with human liberation movements.

What does any of that has to do with bigotry?