You're offended because of the suggestion that your comment about the extent of free speech we have with respect to protesting the NSA might be motivated by you

You're offended because of the suggestion that your comment about the extent of free speech we have with respect to protesting the NSA might be motivated by your own previous work experience with the NSA. Even if true, I wouldn't say this indicated you were a shill, because shills are generally paid to push propaganda. People are naturally biased by their experiences in positive or negative ways. You made what could be construed as a pro-NSA comment in an environment dominated by anti-NSA sentiment, and somebody made an assumption that maybe you had a good experience working at the NSA and wanted to clarify it. For what it's worth, it never occurred to me that you were a shill or a former employee, the suggestion is absurd and totally out of left-field.