It seems to me that troll activity actually prevents free speech in some instances. I wonder how many people - especially those in the public eye deliberately refrain from expressing their support for the McCanns because they have seen what happens to those who do - Aled Jones being a prime example.
Considering what I have seen in the past I have to strongly agree with this. The best outcome for these people who take it upon themselves to behave in this manner seek to destroy debate or even intelligent discourse by the use of inflammatory remarks or simple abuse. They are using it to quite possibly render people silent and their opinion is the only one that should be talked about and repeated over and over again. Any dissent or alternative view is simply not tolerated.
Twitter have a shameful record I think regarding all manner of abuses that take place, I do believe the technology must exist but as yet have not implemented it or choose not to. Even if you report comments that are clearly a breach of the terms and conditions, only very rarely is some direct action taken as a result.