But veganism? It doesn't hurt a cow to utilize her milk or a chicken to eat its eggs. So what is a vegan's valid argument?

Ebbie,

The arguements that I've heard (not mine, I'm a confirmed omnivore) are basically these:

In order to keep a cow in milk, it must bear a calf every year. This is apparently cruel. Male calves have no use in the system, so are killed at birth. Again cruel.

With chickens it's largely down to the conditions in which 'battery hens' are kept, which is cruel. Again male chicks are useless, so are killed. Quite how they manage to argue against people who keep thier own free range hens is beyond me.