A market that allows insiders to profit from still-hidden information, inevitably at the expense of non-insiders, is not truly free. And legislators privy to non-public information from hearings are definitely insiders in any rational sense. The fact that they're not so in a legal sense is only a reflection of the fact that they write the laws and sometimes do so for their own benefit. As the saying goes...

There are two groups of people who laugh at the law: those who break it, and those who make it.