@Kshatria the issue is not his level of greed, it is his level of incaution. He is the weakest of the weak delver (as far as he knows. but like you said, this is a plot armor and misunderstanding-genre story...), with a subpar weapon that will break before he even does a proper attack (clearly not up for even hurting an earth dragon, even if he aims at the eyes), and no armor. Even worse as he is dragging someone he clearly cares about into the danger as well. He might be talking about a secret weapon, but I really doubt it will be something he thinks is up to the task of slaying a dragon specced for defense in a single hit (he said he collapses afterwards), and with how he carries pretty much nothing, I will be surprised if it doesn't involve using his "trash"-spear.
Charity is a privilege of those that can afford it, so if he is not strong, he shouldn't charitably try to leverage his combat ability for others sake. Had it been a sacrifice to lure it away as bait, then fine, it is his own lives (plural yes, he literally owns the slave) to do with as he wishes. But he clearly hopes to survive.