There it is: dwarves are not heroes, but calculating folk with a great idea of the value of money; some are tricky and treacherous and pretty bad lots; some are not, but are decent enough people like Thorin and Company, if you don’t expect too much.p. 213
That phrase, “if you don’t expect too much” is what keeps dwarves from being heroes. You can’t count on them. Their calculations may or may not take you into consideration. A hero’s calculations always take other people into consideration. It’s not that Thorin and company were rogues. They cleaned up after their unannounced dinner party at Bilbo’s without being asked—but then they left breakfast “a fearful mess” (p. 37). One wonders if the first was to help gain the “burglar’s” service while the second was because they thought they had already obtained it.
But heroes do consider others. Paul says it this way, “Do nothing from selfishness or empty conceit, but with humility of mind regard one another as more important than yourselves.” A hero does that, certainly not always perfectly, but however corrupted, this regarding others is part of his DNA. Gold is in a dwarves DNA. And they know, in moments of sanity, that this hinders their joy of life.