My friend owns one... He's very sweet, and he's being trained for dressage and some jumping. She found him abandoned by his herd as a foal.
And in a game reserve there's a herd of very tame, very sweet zebras. But they are not rideable, just because no one wants to take them and train them, we prefer to have them still "wild".
So zebra's are actually wonderful pets, if trained correctly, but they are not dangerous. They WILL "attack", but only if they are wild and you are posing a general threat to their herd, and it's mostly the mares with young foals or the stallions. The unbred mares or those with older foals don't have a problem...
This is the "tame" herd I mentioned above. Even though the mare has a very young foal (pictured), you will see that neither her, or the stallion or older foal have a problem with being close to us: P1030774.JPG P1030782.JPG P1030817.JPG P1030823.JPG