Who would gain from a law that bars you from paying your lawyer more than 25 percent of the money she wins for you in a lawsuit?
Think about it. If you have a case worth $X, a lawyer will take it on a contingent fee basis only if he thinks he can collect the $X before spending more than his % x $X fee. He won't agree to represent you if he expects to invest more than his contingent part of the eventual recovery, if any.
But wait. The case involves risk, right? You might lose; and, even if you win, the guilty party may go bankrupt. Why would the lawyer take your case unless he gets back his investment plus something extra for taking on the risk?
In the real world, chancier cases demand bigger contingent percentages. But the source of the risk doesn't matter. Risk of uncollectability. Risk that getting to trial — or completing appeals — will take years, delaying payment. Risk that controlling law may change. And of course risk that a judge or jury may decide against you.
A cap on percentages would kill off riskier cases, including strong ones.
The U.S. Senate today voted down an amendment that would've limited contingent fees in medical malpractice cases to 25 percent of recoveries above $150,000. Yay.