And then people wonder why a whole swath of society is for tearing down public institutions, buys into conspiracy theories and is willing to elect the most unqualified people.
First, unless we are going to limit ourselves to hiring government lawyers for regulatory agencies fresh out of law school where else are we going to get lawyers with significant experience in the field that agency regulates?
Second, especially for political appointees, these government jobs are usually temporary. Where do you expect an experienced say antitrust lawyer working for the government to go when that gig ends?
It really isn't unusual for lawyers to work both plaintiff and defense in the same field. Major law firms often take cases from both plaintiffs and defendants in whatever fields their specialize in.
It might be possible to build a system where there is no switching, but it would have to be quite different. We'd need some way for you to go into government early in your career with assurances that you can stay there for the rest of your career. I can't see a reasonable way to do that.
Prior to the current administration at least, staying in government work for an entire career was more than possible and let's be clear: tons of people do stay in these jobs. Not every government lawyer, SEC employee, etc. goes over to the "dark side".
The problem is not that there is no ability to stay in public service; it's that the financial rewards of going to the other side can be massive and for the most ambitious and money and power-driven, this is a problem because the system isn't nearly as resistant to corruption as Americans would like to believe.
People with intelligence, skill and drive can use public service as a path to lucrative opportunities working for companies and organizations that are diametrically opposed to the public interest.
> Major law firms often take cases from both plaintiffs and defendants in whatever fields their specialize in.
This actually isn't really true in the way you're suggesting. For example, you won't find firms that handle consumer class action defense filing class action lawsuits on behalf of consumers, you won't find firms that sue employers over wage and hour violations also representing employers, etc.
That's why firms in these markets are known as "plaintiff-side" or "defense-side" firms.