Final answer:
In feudal Europe, simony and nepotism were destructive because they compromised the spiritual integrity of the Church and caused conflicts by undermining the moral authority of church officials and creating a hereditary priesthood against church doctrines. These practices led to significant reform movements and clashes with secular powers.
Step-by-step explanation:
During feudal Europe, simony (the selling of church offices) and nepotism (favoritism based on family relationships) were seen as particularly destructive from both secular and ecclesiastical viewpoints. Simony undermined the spiritual integrity of the church's leadership by turning sacred offices into commodities that could be bought and sold. This practice led to the appointment of church officials who were more interested in wealth and power than in spiritual matters, thus eroding the moral authority of the Church. Nepotism was damaging as it established a hereditary priesthood that contrasted with the Church's doctrine, and it often led to the secularization of church roles as well as dynastic control over religious offices.
Efforts to reform these practices were led by movements such as the Cluniac reform, demanding that bishops be elected by clergy and insisting on clerical celibacy. This clashed with the feudal lords' desires to control ecclesiastical appointments for their own gain, leading to conflicts such as the Investiture Controversy. Emphasizing the importance of spiritual legitimacy, the Church could excommunicate kings, threatening their rule and inviting rebellion. The Pope's declaration stripped monarchs of their control over the Church, leading to an enhancement of papal power and the diminishment of secular authority in ecclesiastical matters.