Do Federal employees have free speech rights? My father was a mail carrier when I was growing up, and according to the union's material that they mailed to the mail carriers, Federal employees don't have free speech rights and that was how Reagan was able to fire the striking air traffic controllers. Mail carriers are not able to complain about working conditions in the post office (that is what the union mailer was complaining about, I guess since a union staffer was writing it they could complain -- it was like 25 years ago that I read this, so I could have the details wrong).
The Hatch Act[1] restricts the ability of Executive branch employees to engage in partisan politics. The Smith Act[2] prohibited executive employees from advocating the overthrow of the US Government, although I think it's been found unconstitutional.
Note that I'm 98% sure that it's still illegal to advocate the violent overthrow of the government, so civil servants should take the Smith Act overturning with a grain of salt.
When you get a clearance, you sign certain pieces of paper that contractually waive certain rights with respect to that information you are cleared to receive.
You also obligate yourself contractually to a number of other responsibilities (some, depending on clearance, for the rest of your life).
Because it doesn't affect you or any other person or organization that doesn't have legitimate access to classified information.
The key words here are "unclassified government systems". There are rules and procedures to make sure that the classified stuff stays on the classified systems, and one of those, very sensibly, is that classified stuff shouldn't be on the unclassified systems.
