I knew of some factors that made contractors' employees easier to fire -- generally non-unionized, particularly in a right-to-work state like Virginia; lacking statutory protections given to civil service employees -- and therefore preferable despite the higher cost of contracting. However, I'd never thought about the First Amendment aspect. Private sector employees can be fired for publicly disagreeing with their employer, even on a matter of public policy. Law student bloggers shouldn't post about a case in opposition to their employer's stance. (Though I think writing in non-legal terms about a corporate client with whom you haven't worked and is OK; some firms have so many clients in a particular sector that you'd never be able to complain about the bad smell on a flight, or a fight with your cell phone provider, if you observed a blanket ban.)

Government employees usually cannot be fired simply for disagreeing as long as the disagreement doesn't affect their work performance; a policy that paralleled the private sector's would mean that you'd lose your right to free speech upon receiving a taxpayer-funded paycheck. Christine Axsmith's paycheck had "BAE Systems" rather than "Central Intelligence Agency" on it*, so she could be fired for her weblog, though it was posted on Intelink, the intelligence community's classified intranet, and therefore available only to people with top-secret security clearances.