That's an easy question: As a general rule, more eyes=more security. Rear lots have fewer eyes because passing motorists, pedestrians, and cyclists can't don't pass by it. In addition, neighboring storefronts usually won't have a view of the parking lot either. Additionally, the enclosed area and restricted viewing angles that makes up many rear parking has a psychological effect. It makes criminals feel safer, thinking they have cover. It also makes customers feel less safe.
Yes, there are still people coming and going from the store to their cars. And crime can of course happen in front parking lots as well. It's a matter of degree. Rear parking lots can be perfectly safe.
I honestly think that security needs to be a consideration in the design of parking, but shouldn't be a trump card. The security/safety really depends upon the implementation. Careful planning and a little investment in lighting, surveillance, and security personnel can counteract any security concerns.
Right, I agree, it's all a matter of appropriate design. On a side, but related note, quite frankly, in this day and age, I have my doubts as to how much help you can expect from a passing motorist. I read a story in the paper the other day about some fellows who ran across a busy street to help a lady who had fallen out of her wheel chair in spite of the fact that a couple of dozen people on her side of the street walked right past her.
Are the people who have a problem with rear-facing parking lots forgetting about all the Wal-Mart-type store robberies and abductions. And the above post makes a very good point: who in today's society WILL help someone in need?