Final answer:
An 'unbiased opinion' may seem oxymoronic if it implies that the neutrality of the opinion is affected by being asked politely.
Step-by-step explanation:
The phrase 'He is always able to give an unbiased opinion when he is asked politely' poses a potential oxymoron because it suggests that the ability to remain neutral and provide an unbiased viewpoint might be influenced by the manner in which the request is made. If politeness can sway his ability to be unbiased, then the opinion might not be entirely free from bias. The quotes from various sources in the question exemplify different aspects of character and perspective, ranging from fairness and generosity to earnestness and sincerity, all of which relate to the broader discussion on how one's disposition can be influenced by personal experiences, social context, and interpersonal dynamics, ultimately affecting the way opinions are formed and expressed.