That people feel less comfortable expressing all their beliefs than they used to doesn't tell us much about the state of free speech in America.
Kind of makes you wonder whether a poll so constructed was designed at the outset to reach a specific conclusion, doesn't it? :)
If you feel comfortable voicing your political opinions all the time in front of friends and colleagues, you either need more interesting political opinions or a more diverse group of friends and colleagues. Common sense self-editing is not a sign of lack of free speech.