It seems as though your approach to this stimulus is slightly overwrought. Remember that there is great value in simplicity, and the more precise and concise you can be with your analysis, the faster and more accurately you will find the credited response. It is not uncommon for the LSAT writers to make concepts or ideas in the premises somewhat abstruse or byzantine in an effort to confound your ability to remark the most important elements.
You could diagram this stimulus as follows:
Political regime that censors
censors perceived threat to power
Conclusion: Political regime that censors
censors material that decreases public passivity
Notice that your premises and conclusion are reversed. The author assumes that material that decreases public passivity implies a perceived threat to power. Also, I have kept my terms as consistent as possible between the premises and conclusion to avoid introducing sources of confusion or ambiguity. Likewise, I dispense with the irrelevant parts of the stimulus (those that do not help better understand the underlying structure). Finally, I would not necessarily symbolize such a problem on the test as such work could in fact confuse the issue for you. Your goal should be perhaps to talk yourself through a problem like this with the intention of discerning the gap in the reasoning without resorting to a possibly erroneous symbolic representation of the logic involved.
Symbolization is a powerful tool but is a complement to and not a substitute for your own analysis of the reasoning contained in a stimulus. You must give a concise and accurate description of the reasoning in a stimulus before you symbolize it, and in a case such as this, it might be better not to symbolize at all when actually taking the test.