It's not really any more difficult to keep your nutrition balanced as a vegan than as a carnivore. Either way, you have to pay a bit of attention to what you eat, not eat too much of this, and not eat too little of that.

And what's wrong with taking supplements? You keep invoking the concept of "natural", but there is nothing intrinsically superior about nature. Humans are in control now, and we're doing a lot better for ourselves than nature ever did.