To quote Terry Pratchett again:

““History was full of the bones of good men who’d followed bad orders in the hope that they could soften the blow. Oh, yes, there were worse things they could do, but most of them began right where they started following bad orders.“ 

I think Balon Swann is a typical man of his class who never quite learned to think for himself beyond the ideas deemed appropirate for men of his class. 

He’s not among the worst – he’s not a partisan, he’s not a coward or a sadist or a bully, he’s one of the few people who speak in favor of Tyrion (although he’s easily outmanuevered in court), he snarks back to Jaime about the proper conduct of a Kingslayer…

But he also (at least in spirit) fails the more difficult test of what to do if you’re given an order that violates the tenets of knighthood when he’s faced with Cersei’s order to be complicit in the murder of a child by bearing false witness as to his murderer.

Something tells me he’s going to be tested even more strongly at Starfall.