Because it will force THEM to finally have to pay taxes themselves since the tax will be on purchases and not on "income".
You forget they won't have to pay taxes on capital gains and estate taxes so they may very well support the Fair Tax.
With the tax shelters, their fortunes are not "theirs" but belong to some phantom entity that won't be taxed. This corporation though is what spends the money for all the parties, the yacths, and whatever to the tune of millions/year all tax free to these politicians/lawyers. The fair tax simply taxes money as it leaves the bank - immediately upon transfer to another entity.
It is the consumer who drives the economy and ultimately decide which companies stay in business and which one's fold. Our current tax structure taxes money before it enters the wage earner's wallet. The Fair Tax taxes money as it leaves the consumer's wallet but can put more money in the bank if the wage earner chooses.
One of the problems I have with the fairtax is this: With the implimenting of a huge federal sales tax do we still pay the state sales tax? if so, our sales tax could be more like 40%. Also, I understand that we would only pay sales tax on items once, so a new car buyer would pay the tax, but the used car buyer wouldn't pay it at all. Who in their right mind would buy a new car?who would buy anything new that they could get used? And second, I could see the employer who normal hires someone for 10$ an hour cutting his pay scale for any new hires to 7.50$. I think this could be a problem. I think that most places will pay the least they have to and if there are people willing to work for 7.50 then they won't pay 10$.