It comes down to this: to whom are you speaking for? For yourself and your own views? For your agency and a cleared governmental policy? Who is the audience and how will they perceive your comments? The bottom line is that anything you say that has to do with work will be perceived as government policy and you will be seen as a spokesperson for the government, your department, or your agency. Most folks see the "government" as one big blob, and anyone who is from the government that says anything must be speaking for the government.
A few years ago I was interviewed by CNN on a fairly contentious issue. I went to a studio over near Union Station in DC. I was the only person in the studio. The cameras moved around by remote control and the interviewer was in California. She was someone I had talked to several time before, and had met when I was in California. I stuck to cleared language during the interview, and it went as planned. The Interviewer thanked me and the interview was over as I perceived it. I relaxed. The CNN correspondent and I then bantered a bit about the weather, our families, and a few other non-work issues. She then asked me what I really thought was going on with the issue. My answer was off script and not cleared, as I did not see it as part of the interview. Guess what was on CNN that night? It was hard lesson, and one I will never forget.
Freedom of speech. Absolutely! You have the freedom to make a complete idiot of yourself! Just remember, whatever you say will be perceived as official policy.