Nixon, Bush, and Reagan are all serving, or did ,serve prison terms for their illegal speech right?
No.. Do you think they were or are you being rhetorical?
Each of these guys are also in authoritative positions which can require people to follow their whims, unlike the person TFA discusses who is not in an authoritative position.
There is little to no clear evidence that they told anyone to do anything but the circumstantial indications are that they did. For Reagan, there was no criminal punishment for the Iran Contra affair- for bush, no laws were seen to be violated, and for Nixon, obstructing congress by deleting 18 or so minutes of a recording is the only thing linked to him outside the testimony of a known democrat (Dean) who was getting favorable treatment for that testimony. And since Nixon, it would seem that the white house regularly tells congress to STFU by claiming executive privilege which is about the same because they still do not get what they asked for. This all impacts the ability to prosecute if any laws are known to have been broken.
I don't think you can compare the two (or four) situations. Maybe a more accurate comparison would be all the accountants who devise schemes to dodge and defeat tax obligations. Whether right or wrong, a law exists that allows prosecution of someone who conspires to commit fraud on the government and they his teaching for the specific purpose of defeating FBI employment polygraphs seems to fit that description. Typically conspiracy charges crosses from free speech to criminal when someone takes steps further than talking about it. For instance, if you and a friend were sitting around smoking a joint talking about how easy it would be to rob a bank, it would be free speech. If you or your friend started staking banks out and purchasing supplies you discussed, it can become a criminal conspiracy whether you actually robbed the bank or not. Of course either of you would have to be aware the other was taking steps to make it stick.
So perhaps this is a good thing that this guy is being prosecuted. Perhaps it is going to end up changing the law or how it is applied in the future which seems to be misguided or misapplied in this case. Perhaps it is going to end the reliance of lie detectors for government. I think either of those would be a good thing. I'm just sorry that one guy will have to shoulder the brunt of the work.