The God does say in the bible He has plans to prosper us. But the prosperity spoken of in the bible is not the same view that a lot of people have. Joel Osteen's entire ministry is based on the gospel of health and wealth. If you follow God and have a good relationship with him then you will not be sick, and you will be wealthy, anything less is not living in total victory. Number 1, the bible never mentions anything about how we will live in total victory. Number 2, prosperity and wealth are not the same thing. Prosperity is God providing for us exactly what we need, when we need it. As for no sickness, that's just a misinterpretation of the Lords prayer. Rather than reading "your will be done on earth as it is in Heaven" a lot of teachers assume it should be "your will be done THE SAME on earth as it is in Heaven" One look at the news and I think people will realize the plans and life God has for us in Heaven are not the same as they are on earth, so just because there is no sickness in heaven doesn't mean there won't be any sickness on earth.
The reason a lot of these teachers are popular is not because of their faith or relationship with God, but because of the fact that they preach a ministry that makes people feel warm and fuzzy all over. They don't preach the gospel, they teach a "How to get rich and stay healthy" plan. Our eyes should not be on the things of this world, but on eternity. Living life today is not about getting rich, and living life fully here on earth, but living life fully in eternity. I don't support arguing and dissension in the church, but I also have no issue with teachers being called out when they're wrong. They should be, for their benefit so they can learn, and our benefit so we know unbiblical teaching when we hear it.