One of the biggest gripes anyone can have against organised religion, and this spans a variety of people including even religious people- is the grandiose wealth amassed by those in charge, often at the expense of the poor people who keep sinking their money in, hoping for a better life.
Even worse than these people, in my opinion, are the other ordinary people who decide to defend them when anyone raises questions about their extravagant lifestyles. Pastors living like rockstars, when Jesus specifically instructed taking care of the poor and needy above all else, and giving away your fortune if you want to follow his footsteps.