Working in the government means that eventually you will receive information that the public hasn't received yet. After receiving this information, any competent person can no longer continue trading as if they hadn't receive that information - their actions will inevitably be influenced. The only way to avoid that scenario is a blanket ban on the trading of stocks.
This doesn't mean that the government will be a "club for the wealthy", in fact, it will do the opposites. Congressmembers will no longer earn millions off of trading stocks at the expense of the working people.
Blind trusts and discolsure rules already exist, but they haven't resulted in any meaningful change. Now, officials just blatantly engage in insider trading without repurcussions. We need a blanket ban to resolve that issue.