You don't survive long in the Underdark with principles if you're not willing to compromise them on occasion. Olard's not upset about 'stooping to their level' specifically so much as that he had to because his strength and size failed him. His defining principle is that strength should be used to protect people who are smaller and weaker; this is a situation where protecting his allies means abandoning his tenet of strength > all, which is very demoralizing.