Is it not cruel to nail horse shoes on?

No, it isn't cruel at all. there is literally no feeling in their hoofs. It would be like if your nails were 1/4 inch thick and you grew them out to be an inch long and then pierced them, since people like really wacky piercings, you wouldn't feel a thing because there are no nerves or any kind and their purpose is to protect that part of the body.

Nope, it's like cutting your fingernails with clippers. There are no nerves in the hooves where the nails go.

it is NOT! i have a horse of my own and it doesnt even hurt my horse when she gets her shoes nailed on!

A shoe correctly fitted by a trained farrier is better for a horse than it to be left unshod.

It is only if ill fittling shoes are left on a horse any problems are liable to occur .The nails go into the dead part of the hoof . By dead I mean like a human nail.

I personally have shod hundreds of horses, grew up around them my whole life and have NEVER seen a horse irritated by a correctly positioned(nailed)shoe. Infact, there are many happy horses who have jobs they enjoy where their feet have to be protected and by shoes. As is the case with the mounted patrol,or any animal working on pavement with extra pads under their shoe to absorb shock. Also horses with medical conditions such as founder or navicular who's feet need special care benefit from shoes. I think there are many cases where it is worse for a horse NOT to have shoes! And don't worry about the nails, Their location is in non-living tissue, like your hair or thumb nail. It is little more than an accesory to them! Remember, we are talking about a 700lb plus animal here!