Unlike Thomas More, the Duke of Norfolk isn't a man of the mind—he's all brawn, all the way. In other words, More is the Brain; Norfolk is Pinky. No shade intended.
To be honest, though, Norfolk is a great friend to More. We see evidence of this in the pair's playful banter in the opening scene of the play, but we don't understand the full extent of their bond until More gets into trouble with the authorities. Unlike the other members of the aristocracy, Norfolk actually wants to help More—even if that means convincing him to turn against his deeply-held religious beliefs.
Unfortunately, that plan's doomed from the start—this is More, we're talking about—and Norfolk ends up abetting Cromwell's persecution of More in a small but significant way. So why does he do it? Why does he betray his best friend? It's a tough question, but we think this quote sheds some light on the answer:
NORFOLK: [...] Goddammit, man, it's disproportionate! We're supposed to be the arrogant ones, the proud, splenetic ones—and we've all given in! Why must you stand out? (Quietly and quickly) You'll break my heart. (2.417)
While Norfolk respects More's unwillingness to compromise, he also hates it because it highlights his own relative spinelessness. Ultimately, it's this shame in the face of More's unflinching goodness that leads Norfolk and his fellow one-percenters to passively aid Cromwell's evil shenanigans.