"Completely healthy and nutritionally complete" debatable. Vegan diets are discouraged significantly for pregnant women and children because of how damaging calcium, zinc, and B12 deficiencies can be during that time. And even if you aren't a pregnant woman or child, you still have to deal with the various deficiencies that come with that, typically by eating very targeted foods or highly processed and manufactured supplements that also have problems, such as availability, allergies, cost, or simple difficulty incorporating into diets (e.g. you can't exactly use algae oil like you would olive oil, you can't sprinkle flaxseed on everything).
And speak for yourself with regards to morality. Humans evolved as omnivorous creatures, just like millions of other species. I feel no moral obligation to eliminate animal food sources from my diet. The opposite, in fact. Because a vegan diet is effectively an abandonment of culture. I'm not going to stop making Pasteis De Nata or Caldo Verde simply because you feel bad for the animals. Letting my culture wither away like that is a far bigger sin in my eyes than eating animal-derived foods, which we evolved to do.