MORE: Go he should, if he were the Devil, until he broke the law.
ROPER: Now you'd give the Devil benefit of law!
More explains that Rich, in a sense, has a right to be bad unless he finally breaks the law. But, in the end, Richard really will violate the law by committing perjury and sealing More's death sentence. That's the nature of cynical power-grabbers like Rich: They can manipulate events behind the scenes without visibly doing anything wrong and take advantage of the principled man's good nature.
MORE: Yes, what would you do? Cut a road through the law to get after the Devil?
ROPER: Yes. I'd cut down every law in England to do that.
MORE: And when the last law was down, and the Devil turned on you... where would you hide, Roper, the laws all being flat? This country is planted with laws from coast to coast... man's laws, not God's, and if you cut them down... and you're just the man to do it... do you really think you could stand upright in the winds that would blow then? Yes, I'd give the Devil benefit of law for my own safety's sake.
More explains that he recognizes the necessity for the kind of law and order that the king represents. There needs to be a secular authority—even if it provides a refuge for scoundrels like Rich and Cromwell. Of course, those laws end up betraying More and leading to his execution, instead of keeping him safe. So maybe, in retrospect, he should've run away to Italy or something.
ALICE: No. If I'm to lose my rank and fall to housekeeping, I want to know the reason. So make a statement now.
MORE: No. Alice, it's a point of law. Accept it from me... that in silence is my safety, under the law. And my silence must be absolute. It must extend to you.
Technically, according to the law, More's silence isn't really a crime. As More later tells the court, silence implies assent rather than objection (even though he really does object to the king's oath). It's only when Rich lies and claims that More wasn't silent that his fate is sealed.
BISHOP: Just so. Sir Thomas, it states in the preamble that the King's former marriage to the Lady Catherine was unlawful... she being his brother's widow and the Pope having no authority to sanction it. Is that what you deny? Is that what you dispute? Is that what you are not sure of?
DUKE: Thomas, ye insult His Majesty and Council in the person of the Lord Archbishop!
MORE: I insult no one. I will not take the oath. I will not tell you why I will not.
DUKE: Then your reasons must be treasonable!
MORE: Not "must be." May be.
More refuses to take the oath, and tries to survive on a technicality. Since they don't know that his reasons are treasonous, they can't actually determine that he's treasonous. (However—his reasons actually are treasonous in the king's eyes. So More's persecutors aren't wrong.)
CROMWELL: […] Is there a man in this country [...] who does not know Sir Thomas More's opinion of this title? Yet, how can this be? Because this silence betoken... Nay, this silence was not silence at all, but most eloquent denial!
MORE: Not so. Not so, Master Secretary. The maxim of is "Qui tecat consentere." The maxim of the law is "Silence gives consent." If, therefore, you wish to construe what my silence betokened... you must construe that I consented, not that I denied.
More claims that his silence should be interpreted as consent—even though More really isn't consenting. Although he's a principled guy, he isn't above using a clever and somewhat misleading legal strategy to save his skin.
CROMWELL: Is that in fact what the world construes from it? Do you pretend that is what you wish the world to construe from it?
MORE: The world must construe according to its wits. This court must construe according to the law.
Cromwell gets owned. Here, he's making the somewhat unsophisticated argument, "Hey, c'mon! We all know what More thinks, right?" But More totally beats him down by pointing out that that's not a legally sound argument.
VOICEOVER: Thomas More's head was stuck on Traitor's Gate for a month. Then his daughter, Margaret, removed it and kept it till her death. Cromwell was beheaded for high treason five years after More. The Archbishop was burned at the stake. The Duke of Norfolk should have been executed for high treason... but the King died of syphilis the night before. Richard Rich became Chancellor of England... and died in his bed.
The same corrupt system that killed More ends up killing most of the men who orchestrated his killing. Ironically, the only one who dies in his bed, aside from Norfolk, is Rich—probably the worst and most dastardly of the bunch.