Why shouldn't a server use a glass to scoop ice?

The glass may break or chip.

A server shouldn't use a glass to scoop ice as the glass may break. This is due to the potential temperature difference between the glass (which may be room temperature or hotter if it is taken from a dishwasher), and the cold ice. Any existent hairline fractures in the glass may then expand and crack, whereby the smashed pieces of glass could then land in the client's food, table or lap, potentially causing injury to the person.