"For what shall it profit a man, if he shall gain the whole world, and lose his own soul?" Mark 8:36 (KJV)
God Himself sits in judgement over the souls of men But His patience is eternal... not so the IRS. To the tax collector, the letter of the law is the Final Arbiter what Sits o'er All. And into yon letter the American constituency and its elected elite have carved, jointly and severally, an exception from taxation so deeply etched that only the most hard-bitten secularist would creak her jaw to call it a "loophole": churches shall pay no taxes.
Of course, Old Scratch hangs his hat in the details, so they say. Church organizations aren't on the hook to the Treasury, but that doesn't necessarily extend to preachers' spouses or their kids. So as Kenneth Copeland can attest, if you find yourself getting a little too cozy with political aspirants, expect the State's Infernal Revenue Service mephits to hound you till the rivers run red with the blood of the innocent (or from 2007-2011, whichever comes first). Similarly, if you minister to a huge congregation and if they tithe, and if you turn that lucre into comfortable mansions, plush lifesytles, and dalliances with aristocratic and oligarchic elites, you probably shouldn't be too agog when (not if) you run afoul of ordinary folks' ordinary moral sentiments.
In Aristotelian terms, it ain't proportionate for a loquacious preacher to amass wealth that would make Solomon blush and to then be given special dispense from the state, most especially when the underlying religious tradition has strong overtones of modesty, service, and charity.
One of the best lessons I ever learned from a Munger lecture is that accumulated wealth is a byproduct of exchange. It's effluvium, waste, all those ledgers cramped with artifacts of past exchanges. What we should care about, what produces satisfaction is the exchange itself that gave rise to plump capital holdings. When we focus on the hoard alone, we commit the nasty analytical error of judging outcomes rather than processes, dead artifacts instead of living rules. Anyone drenched in the economic way of thinking (and boy howdy, if you ever need a good example of a natural economist, you could do a hell of a lot worse than bending your gaze towards Mungo) should kick and scream any time there's talk of just or unjust outcomes. Wealth concentration itself is too dumb a bunny to estimate the justice lurking in pairwise exchange. If I drop a dollar in the collection plate, that transaction is part of the covenant I have with God, with my religious community, and with my pastor. That moment of choice (and the moment I initially chose to stand as part of the flock) is where the careful analyst can raise hue and cry should injustice lurk.
Of course, economists will be perhaps more prone than others to punt on any justice that dwells in the collection plate exchange. The epistemological problem of cracking someone's skull open to see if they truly are better off or not making the trade is pretty dang tough. How many people end up regretting religious faith? In which direction do deathbed conversions typically go? But even if we conclude that flim-flam multi-millionaire bs artistes like Benny Hinn provide valuable spiritual services to their congregations, how do we square that with proportional Aristotelian justice? What is the common-sense moral justification for the asymmetrical tax treatment of religious organizations? Do they consume fewer public goods? Perhaps there's a case that churches actually produce public goods on net, beyond the private joys of salvation and community membership mentioned above, beyond the club goods shared by flock members. If that's the case though, wouldn't it be prudent to compare spillover benefits from religious organizations to spillover benefits from other organizations, including for-profit firms? There's a Whole Foods down the street from where I work, and I assure you that the sense of satisfaction I detect in many of the shoppers is almost impossible to distinguish from the spiritual rapture that clings to the faithful I run across on Sunday mornings.
Revisit your null hypothesis. Wealthy preachers might be a symptom that something has gone wrong, but don't let the Devil convince you he doesn't exist: problems happen when we treat a metric as a goal, when we confuse outcomes with intent, when we indulge analytical laziness. Consider whether or not congregants retain the wherewithal to revoke their patronage. Consider if they think themselves exploited. Talk to them if you must. And do please consider that the 16th amendment was a mistake. Perhaps the problem isn't that churches don't pay income tax, but that the rest of us do.