This is really not true with the possible exception of iron, which you can mitigate by eating a lot of citrus (this helps with absorption; plants have lots of iron, but heme iron has much greater bio-availability).
I am not vegan since I eat dairy and eggs still, however this is purely because I enjoy them and not for any particular dietary reason. I allow myself these luxuries while understanding that's what they are: luxuries, not requirements. We are all human, after all, and we can't all be monks who optimize every behavior. I think it's important to be honest about that and truthful about our motivations when we decide to eat animal products, because it is really not by necessity (at least, not in the western world, where plant-based alternatives are affordable and readily purchased).
If everybody ate mostly soy and legumes it would solve a lot of problems, even if they still have a steak or cheese every now and then. But they don't need to have that steak or cheese to be healthy :)
yeah that's because you are indirectly consuming those vitamins that have been given to the animals...
Look at honey - obviously good for you, obviously sustainable, not allowed in the vegan diet.
https://www.vegansociety.com/go-vegan/why-go-vegan/honey-ind...
Humans can live without honey, bees need to survive.
I highly recommend chickpeas and fava beans in particular. Much better for stomach than kidney beans, and perfect for many kinds of rice and pasta dishes. Fava beans are also very easy to grow outside in most climates if you're into gardening and have the space.