You are assuming that the liberals and leftists who would advocate "anything goes" sexually but who would suppress speech that goes against their political views are prone to the rules of logic. They tend to be postmodern in their thinking; to them logic and even language are merely tools of those they consider oppressors in repressing creativity and spontaneity and in establishing the dominance of an oppressive class. They agree with Ralph Waldo Emerson, who said that "Consistency is the hobgoblin of small minds." Additionally, there is the issue of situational ethics, which is the predominant viewpoint among the elite. To those who hold such a viewpoint, there is a "higher value" such as love or self-preservation, that supersede other values. Thus, a liberal who supports gun control may feel no guilt in shooting a burglar because his need for self-preservation supersedes the importance of taking guns away from general circulation. Liberals and leftists also suffer from cognitive dissonance, which enables them to hold to differing opinions at different times. Take John Kerry and John Edwards as examples. One day, they can laugh at the X-rated diatribes of Whoppi Goldberg; the next day, they can pose as upright moral family oriented men.
Whether social conservatives protest immorality a lot, a little, or not at all has little to do relative to the Left's desire to thwart its opponents.