Final answer:
Hythloday refuses to become an advisor because he believes that European courts are too corrupt and self-interested, making it unlikely that his just and idealistic policies would be implemented effectively.
Step-by-step explanation:
The reason Hythloday refuses to become an advisor to a king or prince, as depicted in the discussions of alternative societies like the Polylerites, the Anchorians, and the Macarians, relates to the philosophical discourse in Thomas More's Utopia. In the dialogue, Hythloday outlines his belief that the corruption and self-interest prevalent in the courts of Europe would prevent him from implementing the idealistic and just policies he has observed in the societies he visited during his travels. His reluctance is rooted in a concern that any advice given would either be unheeded or manipulated to serve the political and personal agendas of the ruling powers, rather than contribute to the common good.