[The Squatter of Amon Rûdh]

Surely the Dwarven attitude towards Moria ought to have been enough of a motivation for a group of them to want to recolonise it. Gimli can't stop talking about the place from the moment they enter Hollin, and it seems that the Dwarrowdelf has a strange attraction for the Dwarves of Durin's folk.

Balin, as a wealthy and respected Dwarf, was in a position to mount an expedition to take back the ancient halls of Durin, and my view is that, having regained the Lonely Mountain from Smaug, Balin's mind was drawn inexorably to the greatest Dwarven halls ever to have been lost to a powerful enemy, a place of almost totemic significance to all Dwarves. It's quite possible that he was thinking that if Smaug could be driven from Erebor, then perhaps whatever had driven out the Dwarves of Moria could be defeated in turn. Perhaps the great halls of Durin could be reclaimed, not just for one Dwarf, but for the whole race. I see Dáin's reluctance as a sign that he did not share Balin's confidence. Any king would be reluctant to allow one of his most powerful and respected lords to take a large group of his other subjects to certain death in the pursuit of a dream; even if that dream was the restoration of his race's most glorious city.