I think Janet Reno subscribed to this theory of AG-ship. And we all know what a swell job she did.
FWIW, the AG is the legal agent of the Executive branch -- the job of which is to faithfully execute the laws and responsibilities of government. To do otherwise would result in what you said -- by picking and choosing, AG would usurp the powers of the legislative branch.
Precisely why she should have been impeached. When GOP Hatch had the chance to move, he did nothing but call her "his good friend," the House would never move Articles on her after that big signal. She was allowed to tromp on the Constitutional rights of so many citizens, but the rest of their fellow citizens sat by, did nothing, *too busy* and all that.
The first time the citizenry allowed a violation of the USCon and were appeased with a "We know what's best for you," was the first day this started on the slippery slope we now find ourselves on ... not good.
So then I gather you also agree with my contention that Ashcroft should investigate and prosecute the crimes of the Clintons and their many associates the last 9 years.