How can you be certain that policymakers won't make decisions that help their trading instead of their constituents? The incentive is already there, and the whole thing is legal, too.

Don't get me wrong, I think campaign donations or even more explicit bribes are a huge problem, too, but it is already insane to me that you would ban and prosecute "ordinary insider traders" and just let lawmakers do whatever. If presidents have to give up peanut farming, then asking for congressmembers to be utterly decoupled from stock trading decisions is only fair and sensible in my view.