Timeline: the morning after Tony Stark's discussion
Having arranged a press conference, Captain America stands on the steps of the Department of Justice, hood back to reveal his face, and facing into a throng of cameras (or into the TV for people watching). He has arranged in advance for this conference to be broadcast live on CNN, NBC, BBC News 24, and all the breakfast shows on the East Coast.
"Yesterday, Michael Waller of the CSA, gave me an illegal order to arrest American citizens before the Super Human Registration Act has even been passed. When I refused, she ordered her troops to open fire on me without provocation. I have therefore resigned from the CSA." '.
"The SHRA, like the Mutant Registration Act before it, deprives people of their liberty based on their birth and denies people freedom of conscience based on their abilities. It therefore stands against the ideals of the America I know and love, and against the fundamental freedoms of the Constitution."
"Even were it consistent with those ideals, it would still be a bad idea. The government has been taken over by Dr. Doom and others. The CSA brought us Zero Tolerance and has been taken over by Red Skull in the past. I was replaced by a Skrull a few years ago. I therefore believe that central knowledge of all super powered individuals is a bad idea. Central control of all super powered individuals is an even worse idea."
"I therefore oppose the Super Human Registration Act on both moral and practical grounds. I will tehrefore fight it in the court of public opinion before it is passed. I will fight it in the court of law when it is passed. And I will attempt to rescue those super heroes who will be arrested for nothing more than not wanting to take orders from the United Nations Strategic Hazard Intervention, Espionage and Logistics Directorate" Here Cap pauses to let that sink in, and then continues in a more sombre manner.
"Here I stand. I can do no other."
He leaves a couple of seconds before asking "Any Questions?"
RP Notes: If you wish to interrupt the press conference part way please say where - and if you are watching the conference on TV, please state in the subject of the comment (otherwise, I'll assume that you are one of the gaggle of superheroes who is also a reporter - and is therefore present at the press conference)
[Edited to use the CSA rather than SHIELD]