http://www.ou.org/torah/article/parshat_toldot_6_part_2
...Esav “sold the birthright”. The term used for sold is vayevaz. This is an unusual and ambiguous term. It is interpreted by many authorities to mean “and he sold”. However, Rashi offers another interpretation. He posits that the term means “and he rejected”. Why does Rashi adopt this interpretation?
Ibn Ezra understands the birthright as the privilege to inherit a larger portion of the father’s property. If this is the nature of this right, its sale cannot be viewed as immoral. It is a straightforward business calculation. Ibn Ezra interprets vayevaz to mean “and he sold”. This translation does not involve any moral judgement of Esav’s decision.
However, Rashi agrees with Rabbaynu Avraham ben HaRambam. He explains that the firstborn was destined to be a kohen [priest]. The abandonment of this right is a moral decision. It is a rejection or belittlement of a spiritual opportunity. Therefore, Rashi interprets vayevaz to mean rejection. This implies a moral judgement of Esav’s action...
Interesting. Thank you.