Im not so sure this rendering is accurate:
4 But you, brothers, you are not in darkness, so that
the day should overtake you as it would thieves, 5 for you are all sons
of light and sons of day.+ We belong neither to night nor to darkness.
There may be an error in the translation or the actual manuscript copy. Since the immediate context talks about the day itself coming as a thief in the night, it seems that the verse should actually be saying something like:
4 But you, brothers, you are not in darkness, so that
the day should overtake you as thieves would, 5 for you are all sons
of light and sons of day.+ We belong neither to night nor to darkness.
It's not comparing asleep christians to thieves but rather as victims of thieves - the thieves being the day of destruction that comes unexpectedly like a thief in the night. That's my theory anyway - that there's a translation error or an error in the manuscript.
Also I don't believe the part about them saying peace and security is an actual declaration by the governments. The verse does not say exactly who makes this declaration - or that it's even a declaration, for that matter. I suspect that the verse is simply referring to the fact that the end will come unexpectedly, catching people at a time when they have a complacent, secure attitude - when they feel at peace and secure, oblivious to any coming destruction.
This harmonizes with what Jesus said in Matthew 24 when he said people would be eating, drinking, marrying, building, grinding at the mill and working in the field - all activities that denote normal everyday life at a time of peace and security rather than a time of crisis. Jesus illustrated this by drawing attention to the everyday activities of people. Paul is being more direct and to the point, mentioning that people would be caught by surprise when they least expect - when they feel at peace and secure.