Speaking outside a court in Miami, Joe McBride argued his clients were being "attacked for what they say, not what they've done" and branded the UK "a fallen state that prosecutes its citizens for free speech".
He appeared to reference the case of a woman being arrested for praying outside an abortion clinic, while claiming political activist Tommy Robinson had been targeted "simply for exercising his free speech rights".
McBride also raised the possibility of US President Donald Trump intervening in the extradition proceedings, arguing "he was elected to fight against this kind of nonsense".
He said the pair "remain positive" after speaking to them on Monday.
The Tate brothers, who hold dual US and UK citizenship, were arrested by US marshals at the weekend and appeared before a federal magistrate for the first time on Monday.
They were detained after more charges were brought against them by UK authorities.
Following the brief preliminary hearing, for which the pair wore tan jail uniforms and handcuffs, they will be held in federal custody.
In the coming weeks, a US district judge will consider whether they meet the conditions for extradition.
Andrew Tate, 39, was charged with seven further counts of rape, three counts of arranging or facilitating trafficking for sexual exploitation, three counts of assault occasioning actual bodily harm and 19 additional charges for offences relating to indecent images of a child and extreme pornography.
Tristan Tate, 38, was charged with one count of sexual assault, two counts of rape and three counts of arranging or facilitating trafficking for sexual exploitation.
The UK Crown Prosecution Service (CPS) said the 38 additional charges, in addition to 21 existing charges, relate to alleged offences between July 2010 and August 2017.
The brothers have previously denied any wrongdoing.
"We of course are going to fight extradition," McBride said.
Describing the further charges as "salacious and defamatory," he said: "Some of them are despicable, meritless, heinous and atrocious. They're designed to poison the jury pool, to re-poison public consciousness".
McBride added: "We've never seen a scintilla of evidence that indicates that these guys are guilty of anything. They're being punished and attacked for what they say, not what they've done.
"You can love them, you can hate them, but nobody should go to jail for free speech, and that is exactly what this is about.
"Make no mistake about it, the United Kingdom was once the greatest empire the world has ever known. It is a fallen nation. It is a fallen state that prosecutes its citizens for free speech."
He went on: "That is not what democracies and free societies do. That is what communist China and despotic regimes do. And we're going to fight them at every turn, at every corner, because they are American citizens."
McBride expected the legal proceedings process to take about 60 days.
"Could be a little longer. It could be a little shorter, depending on how it shakes out for us," he said.
"But I think for the foreseeable future, we're in this for the next two months."
