Lawmakers trading individual stocks constitute a serious conflict of interest. The simplest case is a politician can easily see legislation that's about to pass, or even write new legislation, and trade based on how they think that upcoming legislation will affect certain companies or industries before the public becomes aware of the impending changes, thereby gaining a material advantage over the public. This is textbook insider trading. If it's illegal for executives in companies, it should be illegal for politicians too. Furthermore, lawmakers who own a particular stock are heavily incentivized to write laws that will markedly affect those markets and industries, presenting a real conflict of interests. Laws should be made for the benefit of the people, not politicians themselves. These concerns aren't just theoretical either. Lawmakers like Nancy Polosi, Dan Crenshaw, and others have seen significant increases in their portfolios since they entered public office -far outpacing the market in general, and even expert traders who predict markets for a living. This is not a coincidence, and you're going to have a hard time convincing me that these lawmakers just happen to be better traders than expert hedge fund managers.

How would transparency help? It only marginally address the insider trading part of the argument, and it doesn't in any way address the conflict of interest. In terms of insider trading, there are 2 issues I have with the transparency solution: 1. sure you'll be able to see what they're trading and when, which will in theory allow you to follow their trades, but you're still only seeing it after they make those trades so they're still getting in the market before the public. 2. As always, the devil is in the details. Will the transparency be in real-time or will there be a reporting period, as there is now? If there remains a reporting period, that would allow the lawmaker to get into the market up to 21 days before the rest of the public (or however long you make the reporting period). And even if you mandate real time reporting, point number 1 still stands. All of that being said, transparency doesn't even begin to address the conflict of interest portion of the argument. Simply put - if a lawmaker owns a stock they are incentivized to push for laws that benefit that stock instead of laws that benefit the public. It doesn't matter if it's publicly available knowledge that this lawmaker owns said stock or not.

It's not treating every lawmaker like a crook, it's understanding that humans respond to incentives - lawmaker or not. A lawmaker is put into his position with one mandate - affect the public good. Anything that incentivizes them to work against this mandate, or even to work in favor of any other objective, will definitionally result in less public good - and even public harm in some cases. A lawmaker is a public servant, they should not be using their position as a way to enrich themselves