Ah, that old chestnut.
Freedom of expression does not mean you have the right to spout any old bullshit at any point in time. This is the exact same thing as yelling "Fire !" in a crowded theater.
As such, freedom of expression falls under the same blanket of social responsibility. You don't yell "Fire !" in a crowded place because the ensuing panic can get people injured and even killed. You don't encourage people to spread a pandemic virus because God knows there's gonna be some damn fools that are actually going to find that a hilarious idea and do it.
Your freedom of expression is subject to being responsible for what you say. The thing is, on the Internet, nobody feels responsible for anything and they behave accordingly.