I know a person who is an advocate for nuclear energy, who sincerely believes that it is "the power to save the world". He was an officer in the nuclear navy and spent some time working in procurement of naval reactors.

When he retired from the navy he got a job working on small reactors (a subject that he's been passionate about) at a vendor that supplies naval reactors.

The "revolving door" can have the appearance of impropriety but sometimes it's the only way you're going to get people with certain knowledge and talent. For instance anything having to do with naval nuclear power requires a special security clearance on top of an ordinary security clearance. The person who is most likely to have that security clearance (as well as knowledge about naval nuclear reactors) is a person who serves as a "nuke" in the navy. So that kind of person is naturally going to wind up working at that kind of vendor not necessarily because of corruption but because of the scarcity of talent.