Otaaryliakkarnos was a righteous follower of Bahamut that will be need to shown to all humanoid races. Centuries in the past Otaaryliakkarnos' niece was killed by dwarves in one of their old dragonmoots hunt and she still now resent dwarves. She, when was chosen to be part of the Protanther's council, in the guise of human Elia invited a delegation from the Council of Waterdeep to speak in front of the dragons' council. Possibly an adventures' band send by the Council of Waterdeep convinced him to ally to humanoid races to stop the Cult's plot.
Otaaryliakkarnos had great faith in the humanoid races, with only some doubt concerning dwarves. She believed that under dragons' guidance, the lesser races could learn true and correct behavior. She always placed great value on a being's life, and if dragons' lives could be spared by an alliance with humanity, it would be a worthy arrangement.