Final answer:
Simony and nepotism were destructive in feudal Europe because they undermined the authority and morality of the Church, leading to conflicts and significant changes in church and state relations.
Step-by-step explanation:
Simony and nepotism were destructive practices in feudal Europe as they undermined the integrity and spiritual authority of the Church. Simony, or the selling of church offices, turned sacred positions into commodities for trade, hampering the Church's moral credibility and its capacity to serve the faithful properly. Nepotism, the favoritism based on family relationships, led to the ascent of unworthy clerics to positions of power, further corrupting the institution and distancing it from its spiritual mission.
The condemnation of these practices by the Cluniac movement and subsequent church reforms, such as the enforcement of celibacy and the appointment of bishops by clergy, led to conflicts with European rulers who had previously exerted control over church positions. These conflicts played a significant role in the transformation of the Church and European political dynamics, reinforcing the separation of church and state.