Luton built the drop off area within a couple of metres of the terminal building. It has been like that now for years and I can't see why only now you are getting worried about it. I travel through Luton fairly regularly and have done for the past five years and it is very rare not to see armed police in the terminal building and milling around in departures.
As has been said the proximity of a public car park or road to a busy public space is not limited to London Luton Airport. How about any number of places in London.
Gates open and unguarded to airside is a different matter and obviously should be immmediately brought to the attention of the airport security guys.
DeepC