"But if the government can essentially revoke a private individual or company's copyright merely by incorporating otherwise protected text into legislation, that can have adverse effects on copyright holders."

This is a settled area of law; revoking the copyright would be a "taking", inarguably for the public good, and the copyright holder would be entitled to just compensation.

IMO that is the appropriate way to handle this issue; effectively the government uses eminent domain to seize the copyright.