When the church becomes a place of brokerage rather than an organic community, she ceases to be alive. She ceases to be something we are, the living bride of Christ. - Shane Claiborne, The Irresistible Revolution, page 159
Since this all started with Derren Brown's exposé of faith healing, let's go back to it for now. Brown makes a very good point that faith healing is closely tied to the prosperity gospel - this idea that God blesses you depending on your faith. If you're sinning, if you're a "bad" person, you won't get the earthly reward - whether it be money or health. There's a reason this is called the health and wealth gospel. Not only does this put sin in a very odd position in relation to humanity - creating a hierarchy and undermining God's sovereignty - it also turns life into a zero sum balance.
This is the first and foremost negative result of a prosperity gospel: the denial of reality. Anyone who has made it to adulthood (even most who haven't) is aware that sometimes, bad things happen for absolutely no reason. And good things can be the same.
If it sounds like I'm saying "crap happens," that's because I am. To tie wealth (not just riches, but any type of "wealth") to virtue is to obscure the definitions of good and bad. It means, in the health and wealth gospel, that the richest are also the most virtuous - thus, Donald Trump is a hero to the church. People who are rich merely by being born into the right family are blessed by God - the Royal Family in Britain used this logic for ages and they set themselves up as authorities over all of Britannia.
But in reality, you might be born into a poor family, be the most faithful person you can to the Gospel, loving your neighbor, and living a life a free from vice as you can, and you might still be poor. You can be born into a rich family, be a miserly bastard, disrespect everyone around you and have vices by the millions, and you, in all likelihood, will just get richer.
The health and wealth gospel denies the reality that is plain for anyone to see: Life is not fair. The rain falls on the righteous and the wicked alike.
In addition, this kind of gospel puts a lot of power into the pastor's hands. If, say, Benny Hinn or Joel Osteen have a great riches, then they are merely blessed by God for the faithful life they've lived shepherding the flock. Their riches, according to their own form of gospel, mean that they are to be listened to.
This is contrary to the Gospel truth because power was never meant to be concentrated in the hands of just one man. Jesus didn't say to the disciples, "Go and be powerful and get people to listen to you by being awesome." No, in fact, the Gospel lived by Jesus and the disciples was completely different. They lived off the help of others, had a communal purse between all of them, and gave up their careers to follow what Christ was preaching.
The amount of power placed in the hands of someone like Benny Hinn or Joel Osteen or other proponents of the health and wealth gospel is very frightening. It was much worse in the 1980s, when this gospel had its most recent heyday, but it is still a major issue for today's church. The amount of people buying Joel Osteen's books, for example, taking his self-help guruism seriously and funding his empire by doing so, is a way that power is concentrated in his hands. The number of people who travel for miles around to come hear him speak also concentrates the power in his hands.
Instead of a community, what we get in health and wealth churches is ultimately an exercise in individualism. The fact that Joel Osteen preaches getting rid of the bad people in your life is evidence of this very idea - if you are able to cut people out of your life in order to improve your faith, then your gospel is pretty individualistic.*
We live, grow, hurt, love, and exist in community. Ultimately, the health and wealth gospel eschews community in favor of individual growth. And while individual growth is necessary for a person to participate in a community, this growth needs to be facilitated by community, not in spite of it. Just as the selfishness of Randian "altruism" is ultimately unlivable without turning into a morally repugnant jackass, so, too, the health and wealth gospel is impossible to live out without becoming a simulacrum of a caring person. We become "nice" people who do not actually radically love a person regardless of what effect that person might have on us in the future.
Ultimately, both faith healing and the prosperity gospel are closely linked - they are both a Church that begins with "I," not "c."
*I do not mean that if you have a person in your life who is harming your spiritual life, you shouldn't make an attempt to keep that person from harming you spiritually. But that is not the nuanced view Osteen preaches - he preaches that you don't need that person at all, which is contrary to the gospel of restoration and reconciliation.