He imprisons the dwarves because they're on his land, he thinks they've attacked his people and they won't explain what they're doing there - and remember that he remembers the sack of Doriath and the killing of Thingol; he has good reason not to like dwarves but even so, Tolkien does stress that he and his people had standards enough to make sure that their prisoners were properly fed and cared for - he's not an orc.
And yes, he does set out to claim some of what he believes to be an unguarded treasure, thinking the dwarves dead as well as Smaug, and that is a tad aquisitive of him (though on the other hand, who's to say, given the long history of the dwarves and elves, that some of the treasure might have been elvish in the first place, or he might think it is?)
But no moral standards? He turns aside from the march willingly to help the people of Laketown when he realises their plight and he's unwilling to begin a war over the gold alone (the implication, I think, is that he went armed because he was expecting orcs to be staking a claim on the treasure, or simply to turn up at some point, not because he was intending to fight Thorin's company.) I don't think you can say he has no moral standards - seems to me that Tolkien goes out of his way to show both the light and shadow in his character.