I'm not a vegan, and I'm also not a fan of vegan preaching, but veganism extends beyond diet to include other products like clothes and makeup. So it's not entirely a dietary stance, that's just where it gets the most contention. Most people are mostly vegan outside the dietary sphere, so there's not much fighting to be had there.
From what I've seen, this is mostly because white bread is junk food for them. A more natural bread like this is better.
Also the concern with giving ducks junk food is that they'll fill up and not go for other foods, but I remember reading somewhere that that's not the case. At some point they do lose interest in bread (though the leftover bread in the water brings its own concerns.)
To be fair, I'd be skeptical if you told me Andy Griffith was the father of 3D printing.
Though I'd google it instead of asking for evidence first.