John,
yes motorcycle race meetings are usually quite safe, its not the sliding off that's the problem, its being hit by another rider or your own bike that does the damage!! I've seen that happen many a time, it turns my stomach! When he was younger (he's 30 now) I did manage to get him in to aeromodelling for a while, he liked combat, but it was the dozens of photos that I had of motorcycle racing that lured him it to it, and the fact that my brother raced, and an old friend (who was 3rd at the 1969 British Nats in FAI combat) who also raced didn't help.
He's had a couple of seasons racing, but is finding it very expensive. Come off the thing a few times too, only the pride was hurt on those occasions. It cost about £250 to enter a weekend race meeting (4 races) about $400!!
Cheers Neville