I don't think it's cruel, my friend is teaching her Great Pyrenees how to pull a cart so her kids can ride them in fairs(she knows what she's doing so they won't be hurt). I taught my RB German Shepherd, Hannah, to pull a wagon because we have a wood burner and I had to go in the woods to collect wood and trust me it was not fun! It was so much easier having Hannah pull the cart and she loved it! I would know if she didn't because I tried it on Maggie and she hated it so I didn't do it to her again.