Coulter has in the past used her freedom of speech to advocate charging anyone who speaks negatively of the war in Afganistan with 'providing aid and comfort to the enemy' and locking them in prison.
Freedom of speech is not freedom from the consequences of exercising that freedom. That was even literally noted as such in one rather big iteration of the concept (see wikipedia + references).
Example: Dixie Chicks' Natalie Maines saying she's ashamed that then-President George W. Bush is from Texas (like herself), and the backlash against the group that followed.
Note also that although you may be imprisoned, you can still send letters with the exact same speech if you wish - though you may then be indicted for this act and your prison term extended.
Of course under current U.S. (I'm presuming to be the context) laws this wouldn't happen anyway and Coulter was just making some headline-able statements to further her shameless self-promotion, but consider you being in the military and privy to detailed active operation plans. Freedom of speech says you can tell the world if you want to. Laws against treason say you'll be screwed if you do. But those laws don't prevent you from telling the world.. it may be a deterrent, perhaps even a strong deterrent, but you can still exercise your freedom of speech.
Compare this to e.g. a dissident in one of those friendly 'great leader' type states where anybody they suspect might exercise their freedom of speech in a manner they disagree with, they'll just lock them up and allow no communication to the outside world, or indeed the aforementioned soldier on a battleground whose communication may well be monitored and redacted (censored) as appropriate (regardless of the relative ineffectiveness of such measures in this technological age).
What's more worrying than people making use of their freedom of speech (which is almost entirely non-worrying) is the collective power of those listening to said speech and often with it the general lack of responsibility on the part of those making said speech when they are aware of said collective power.
Same example: Though the world was generally not aware of Natalie Maines' statement and it netted but a small column in a UK newspaper, this was picked up by politically inclined groups who lobbied hard to have their songs pulled from 'conservative radio' where individual stations decided individually to stop playing their songs; after touting the overseeing company's line, inciting their listeners, and eventually leading to such silliness as burning of CDs and driving over them with a bulldozer and ultimately a change in the Dixie Chicks' music career (for better or for worse).
In fact, I highly recommend reading up on that particular line of events and maybe buy/rent/download the DVD documentary "Shut up and sing" that follows the group from well before the proverbial shit hit the fan to several years after, as it demonstrates the above points fairly well.. though many people take away many different things from seeing it.. from "there shouldn't have been any consequences" to "good! they should have stayed away from politics!"