I THINK the front one is not required in Louisiana. I thought I remember when I moved from LA to TX we had to go through the pain of getting the front ones tacked on since the cars purchased in LA didn't come with a license plate holder since it wasn't required there. /C.S.B.
There was this truck that got caught a few years ago where the license plate would flip inside and be hidden. The dude got caught after racking up a few thousand dollars in fines and tolls saved. I can't remember what state that was in though.
Most cops don't care. As others have said, you'll find one that will be a stickler. I drive around with no front plate and illegal limo tint but most cops don't care about that either. I figure if I ever get pulled over I just roll down all 4 windows. They're just worried about their safety, re: the tint, so I roll down the windows to alleviate that.
They are not required in Louisiana. I went through the same deal when I bought my car from my aunt in Louisiana. No front plates, and I drove without one for about 3 years with no problems. I did eventually get pulled over for it, and now my front plate is attached with a complex system involving shoestrings.
Having them on the front is beneficial for both cops and citizens. It makes it easier to take down someone's license plate in case of a hit and run, robbery or crime being committed. You can still have a view of the license plate whether you're in front or behind the car.