Won't zirconium veneer damage my opposing tooth since it's so hard?

The porcelain material of a veneer or crown is a harder material and stronger than natural enamel.  Therefore, it could wear down the natural tooth structure of the apposing arch if the bite is not observed and adjusted accordingly. However, a porcelain veneer on a lateral incisor (as apposed to a crown) is usually designed to just fit over the chewing edge of the tooth and will therefore not be in contact with the apposing tooth's enamel.

If these veneers are only on your laterals, then it shouldn't affect the enamel of lower teeth.  However, veneers shouldn't break so easily on the laterals , unless your bite is wrong , or you are grinding.  In that case, night guard would be highly suggested.   

Hi:To some degree all porcelain materials wear down natural opposing teeth.  It's best to wear a night guard to make sure there is no clenching or grinding that would speed up the wear.Best,Dr. Maddahi