Final answer:
Church leaders opposed simony, as it led to corruption and undermined the spiritual integrity of the Church. The Cluniac movement and reforming popes promoted the election of bishops by clergy, and celibacy, and used excommunication to combat the practice. This opposition was part of larger Church reforms that culminated in the Reformation.
Step-by-step explanation:
Church leaders opposed the practice of simony, which involves the buying and selling of ecclesiastical privileges, such as positions within the Church. This practice was seen as corrupt as it allowed wealthy individuals to buy their way into power within the Church, regardless of their moral or spiritual qualifications. The Cluniac movement played a significant role in reforming the church by insisting that positions should be earned rather than bought, encouraging the election of bishops by clergy. They condemned simony as a sin and stated that any clergy member who had bought an office could be removed.
To further ensure the spiritual integrity of the Church, clergy were also required to practice celibacy. This move was intended to prevent church positions from becoming hereditary through children, thus maintaining the sanctity and independence of the Church from dynastic politics. When church reforms led to conflict with European rulers, the threat of excommunication was used to assert the Church's authority over the appointment of clergy and to challenge the practice of simony, ultimately influencing political power structures at the time.