I think its fine. Why is it foolish???
I start all my horses jumping on th long line, using jumps and barrels, logs etc. I think its a great way to let a horse learn to jump before putting a rider on them. They learn they can confidently go over anything from any spot, instead of having a rider interfere or try and place them everytime they jump. Always worked really well for me.
As far as foolish, its not more dangerous than anything else, I have herd of horses breaking there legs trotting around a sand arena. I would just do it and not worry.