So, it isn't really about "ethics," per se, but plausible deniability - send a cutout, a 3rd party the campaign can (wink, nudge) deny works for the candidate, with explicit instructions to shop damaging dirt to news outlets across town. This is merely shrewd Clintonian maneuvering, ethically indistinguishable from doing the dirty work oneself; why the law should think better of this behavior escapes me. (And, I suspect, if the law knew the campaign were pulling the strings in this manner, they'd be right back in legal hot water.)