You have made some interesting arguments, but they are mostly wrong. Let's take them one by one...
In any case, it doesn't help anything when Anonymous and Lulzsec make threats.
Yes, it does. This response and the principal actors wanting to keep their identities secret is a testament to how much influence these threats have. These criminals with badges are scared. I am glad that there is at least fear to keep their abuse of power in check.
Personally I liked the Guy Fawkes image that V put out, but Anonymous doesn't fit it at all, in fact they ruin it if anything.
On the contrary, they are improving it. Guy Fawkes was nothing but a Catholic and a failure. He was caught in the attempt and hanged as a criminal. In addition, he had a cause that few today would identify as a righteous one. Anonymous, by contrast, has fought against government corruption, the Zetas, and even rapists. They are much more upstanding than Guy Fawkes ever imagined being.
Would V espouse silencing his opposition? That's what anonymous does when they DDoS.
IIRC, V was entirely intent upon revenge: "V for Vendetta". He silenced everybody that had any possibility of opposing his plan, but not with a DDoS. His opponents' silence was a bit more permanent.
It seemed to me that V wanted to bring justice and empower the oppressed, if not he would have killed or at least silenced those detectives who were actively working against him, yet he didn't do either.
The detectives were a tool he used. Viewing himself as evil, he wanted to remove himself from the new world he had created, so he used the detective as a tool to kill himself. The detective was no more in control of himself than Brad Pitt's character was in Seven. While V's revenge had the element of justice, it really was an act of revenge concocted by a brilliant, semi-sane, suicidal freak. Anonymous, on the other hand, has mostly been motivated by injustice or entertainment. Either one is less damnable than revenge or suicidal insanity.
Therefore, I must reject your arguments until you base them upon a more solid foundation.