Yes, we should allow zero hour contracts, because some people would rather have a job that is on call than not have any job at all. Additionally, zero hour contracts are positive for people who want to be half retired and only work part time. Sometimes an employer cannot afford to hire a person full or part time, but needs the help on occasion. They should be able to hire according to their needs.
If the employee in a zero hour contract is not given work, they are not paid for the hours they are made available either. This requires an employee to remain open during set times, in the event that they are needed, making them unable to work another job during that time. Standard pay for on-call workers is generally something, and then regular pay if they are called to come in.