My take on this:
There is a purpose to acknowledging free speech as a right.
There is a reason to protect this right.
It is the ability to exchange opinions on the way our political elites manage the affairs of our societies.
We need to be able to evaluate and debate the performance and conduct of government, otherwise democracy cannot function.
Screaming that there is a bomb in a crowded place serves none of the above, furthermore it may result in panic and physical harm, ergo it is punishable behavior.
Likewise, the enabling of haters to come together, reinforce each other's opinions and organize to act on their hatred does not warrant legal protection as "free speech".
I fail to see why it is difficult to understand that coordinating to carry out an attack against an expressor of a political belief is in every way possible different than debating against said political belief.
These are reasons enough for companies that provide hosting services to internet forums to maintain the right (privilege actually) to arbitrarily decide with what kind of clients they want to be associated with.
Other than all of the above it's what Sukiyama posted: