Those who complain about others taking their freedom of speech away realize, or if they don't should realize, the other side isn't advocating for their speech to be taken away. As you said: they are just voicing their opinion. But the thing is: the other side want themselves to have their freedom of speech but they don't want you to have yours. See, we would protect their right to freedom of speech but they wouldn't protect ours. Good example:
Atheists who attempt to create billboards but are stopped by those who feel they don't or shouldn't have the right to express their freedom of speech.
Christians who feel their religious propaganda and scripture should be displayed in public government forums
even though the Constitution prohibits such things.
They want their
freedoms but not have those who oppose them to have theirs. And, they've had successes in doing just that. Not as frequent as in the past but they still have their successes today. And, even though the opposition has some success it hasn't been as successful as theirs.