An employee's personal life often carries over into their work life. If an employer wish to hire someone that is an atheist because he will work Sundays, he needs that information. If he hires a Christian that will not work Sundays, he needs to know. In the case of criminal records, yes. If someone did something once, it is entirely possible that they have the capacity to do it again. Knowing who you are paying is important, not only for efficiency but also to avoid misunderstandings that could have been avoided with more information.
In the day of access to technology and record keeping an employer is just being wise to find out as much as possible about anyone coming into the work force. Potential employees can talk the talk and trump up a resume to get a job. Background checks validate one's word.
If an individual is seeking employment in a job that involves children, they most certainly need to be subjected to a background check. Police officers also should be subjected to a background check prior to employment. Any job where the safety and well being of the public is involved needs to be filled by someone with no criminal past. For other jobs types of jobs, this is unimportant.
I think if it was a violent crime or something, then I understand checking depending on the job. Doing a background check on people just to find out anything about their personal lives and judging them based on things that won't affect their work is completely unneccesary in my opinion.
Criminal convictions are largely permanent, carry heavy consequences. In Panama City, Florida, college students are invited to visit to spend their money, locally. The crimes committed are the same, every year. They are not prevented.
They are actually expected and encouraged because it is the city's only true source of revenue. The effects, for these naive students, could be a problem when entering the job market, later.
At a time when arrests and questioned as justified, and trials minimally fair, it seems like an archaic way of doing things.