There are many uses of the word 'legion'. American Legion. Foreign Legion. A synonym for 'many' of course. I wouldn't use the protesters poor choice of words to put them down.
BTW, here are some other thoughts re: 'Legion'. A little different.
"...Jesus enters the Decapolis, the ten federated cities colonized by settlements of Roman military veterans. He meets the demoniac, a man possessed by empire and death. He’s out of his mind, doing violence to himself and others. He represents all those occupied by the powers of war, militarism and empire. Jesus expels the demons of imperial occupation and frees him.
Legion is my name. What a political statement! A legion was a division of two thousand Roman soldiers. Four legions were based in that area to control the eastern part of the empire."
By naming the possessed man “Legion,” Mark offers a specific parable about how Jesus liberates us from military occupation and empire. Militarism kills us spiritually and physically, as we see in the lengthy description of the possessed man’s violence.
As the God of life, Jesus has come to liberate us. “Come out of him!” Jesus commands the destructive spirit.
Jesus wants to free all of us from military occupation and empire -- the people of Iraq, Afghanistan, Libya, Palestine and those of us here at home, all who are stuck in permanent war and global domination. If we are willing to hear his command, we will find healing and peace.
“Dispatch us into the swine,” Legion says to Jesus. Swine were popular with soldiers, Myers told us in his presentation. The mascot for the tenth Roman legion in Judea at that time was a pig.
Mark describes them as a “herd,” which is not the normal name for a group of pigs. Any reader of the time would know “herd” referred to a large group of Roman military recruits! Here Jesus uses military language and “dismisses” them."
"How are we possessed by the demons of war, militarism, occupation, weapons-manufacturing and empire? How is Jesus trying to expel those demons from us? Do we want to be healed?"
http://ncronline.org/blogs/road-peace/expelling-demons-war