Trouble with this theory is that this implies there actually is a federal regulation you can't walk through Business Class. There however is a rule you can't be in the coughpit. I'd suggest this is a silly post, the law does actually say some fairly specific things about where you can't go and when and the air crew are perfectly entitled to enforce those laws (as they have the right under those laws to do), what they don't have the right is to do is abuse those entitlements in areas to which those rights don't extend.Civil Liberties? You mean it's now written into the US Constitution that all Americans have the right to walk through Business Class?
Let me ask this, if a passenger has the right to walk wherever they want on a plane, where does it end? The galley as the crew are preparing meals? The cabin during taxing or take off and landing? How about the cough pit? Where does it end?
Some passengers are just cough, and that's being polite. Some people love pushing the boundaries for the sake of it, without due thought for the wider consequences!
If you are going to get all uppity about laws and regulations then it's relevant what those laws and regulations actually say and don't just make stuff up. While I understand that people do exactly this all the time that doesn't make it right under the law.