I'm dealing with some issues here like religion, law and order. I want to create a society that believes they're civilised, but may just not be as civilised as they believe.
I suppose what you're questioning here is what we mean by 'civilisation'? It's certainly more than just a technology level. I think you can basically either draw comparisons between the supposedly civilised and uncivilised cultures, or show that the 'civilised' society is fragile and could easily topple and revert, given the right pressures. Questions you might want to think about (bear in mind these are no doubt influenced by my own political, religious and philosophical leanings, etc):
-How do they treat their criminals/enemies? Is an eye for an eye fair or does it make the punisher no better than the criminal? Is executing a murderer intrinsically hypocritical?
-How does the civilisation function under stress? Does it fall apart if there's shortage of resources like food?
-Why are their rulers still ruling? What lends them authority? Fear? Respect? Trust? Were they born to the role, elected or 'chosen' in some other way?
-How do they treat their minorities? Women? The sick? Disabled?
-How open minded are they to other cultures? Do they try to enforce their own ideologies on them, where that might not be best for them? Are your 'barbarians' really barbarians, or do your 'civilised' group just see them that way because they're different to them?