Based on my reading, the leading argument against prosecutions is that it would be imprudent, divisive, poisonous, etc., and therefore an abuse of prosecutorial discretion. I don’t know if that argument will or should carry the day. It seems to me to be an important but decidedly second-order consideration.
Surely the primary question is whether laws were broken; and if there is serious reason to believe that they were, then shouldn’t there be a presumption in favor of investigation? An argument against prosecution that appears to concede that laws may have been broken, or treats the question as an afterthought, seems to me to be unlikely to prevail. The people who strongly oppose investigation and prosecution would be on stronger ground, it seems to me, making the argument that it is simply outlandish and absurd to think that policymakers violated the law. Can that argument be made?