As you've heard variously:
"If the prosecutor is obliged to choose his cases, it follows that he can choose his defendants. Therein is the most dangerous power of the prosecutor: that he will pick people that he thinks he should get, rather than pick cases that need to be prosecuted." (Justice Jackson, via CasablancaPA)
That is a danger. Is this really the most dangerous power of a prosecutor? And how much pause should that give us, given the prosecutor's most serious responsibility? Does the phrase "All come out in the wash" have any application here?