I think Matt Levine’s take on this is best, in that the problem here is _theft_: https://www.bloomberg.com/opinion/articles/2019-03-13/you-ha...

> The real issue is never whether the trading was unfair to the people on the other side; it’s whether the information was misappropriated from its rightful owners

In this case the rightful owners are the American public in whose employ the leakers are. They got this information from their position of trust, and sold that information, to the disadvantage of the people they work for.