As an retired federal agent I completely agree. If you are a regulatory agency like the USDA, EPA, FCC the Department of Education or whatever and you need a high risk warrant served, call the local PD or SO and have them serve it. That's the way it was done historically. There are highly trained people in all the departments mentioned above but they are not highly trained in law enforcement.
What this is really about is not about the glamour aspect of carrying a gun as the writer suggest. Its about getting 6-C retirement coverage and better overtime compensation as a federal LEO.
Only federal employees who's primary and full time responsibility is enforcing the law should be armed.
Using the "Follow-The-Money" rule, I feel that you have made clear the true motivating factor for up-arming all these alphabet-soup agencies.