Depends what you want. You can definitely breed a specific kind of people (ex. Take only people with red hair have the mate only with each other to produce a large population of red heads). That's if you want them to look a certain way. With humans, I think nurture matters the most if you really want to "breed" them to be a certain way. That would likely be most effective if you start from childhood. I'm not really sure if there is a nice humane way to do it though.
Well, unfortunately many many dogs are put to death b/c they don't turn out perfect. Maybe in the future when we've developed the ability to control our offspring's traits, but until then I'm sure it would be the same as dog breeding....
Honestly- humans do this already and don't even realize it. There's a reason we're all collectively taller than just a few generations ago.
Those who are stronger, taller, more attractive get more mates and spread their genes farther. It's why subjective views on beauty in cultures have shaped the actual physiological makeup of those cultures. Light skin is prized in large parts of Africa and Asia. Those with it have a better chance of reproducing in a competitive environment. Heavier set women are prized in most non-Western parts of the world. Here in America blue-eyed blonds are considered highly attractive. Women go for men who are taller and more muscular over shorter, skinnier men. This all affects the gene pool.
Bad idea. Who gets to decide what is desirable to breed for? I do, however, often think that excessively violent people, criminals who are cruel for the fun of it or even torture their victims, should be neutered. That I could go along with.
Who decides the goal? What would be the purpose? Smarter people? Stronger warriors? More submissive servants? Attractive features? Tall? Short? The usefulness would depend upon the goal. As far as there being a humane way, I frankly don't know. If the trials, or rough drafts, were destroyed-that wouldn't be humane.