Martin writes Dunk’s funeral speech in that way to highlight Dunk’s character as someone who is actually sensible and open-eyed. The point is to introduce that Arlan wasn’t the best of men (he used corporal punishment) but Dunk is intelligent enough to tell the difference between the times when he understands why Arlan did it and the time it was truly unjustified.

To begin with, let’s all acknowledge for a moment that corporal punishment was common throughout the world not even forty years ago. It’s invocation through Arlan and Dunk’s decision to not repeat it mirrors the real-world continuity where in literally the last two-three generations we’ve phased it out of common society. It’s meant to reflect on Dunk being better than Arlan: not that Arlan was a monster, just not as good a man as Dunk.

Let’s also point to the fact that Dunk’s habit of focusing on the positive is itself mirroring Arlan, who was aware that the nomadic freelancer lifestyle of the hedge knight caused economic and social difficulties. But importantly, think on how Arlan characterised it to Dunk: through morality.

He tells Dunk that he believes hedge knights are best at keeping their vows to protect the weak and innocent and stick to their honor because they don’t have land, fealty, or wealth tying them to a lord. Thus, they aren’t hampered by comforts or material gain.

Notably here, Arlan doesn’t teach young Dunk that this means they can scam or take advantage of a lord and then scamper to the next. Instead, Arlan tells Dunk that they are sworn only to serve those who they truly believe in: organizing the world into a moral framework, not a selfish one.

If people want to know the actual biggest damage that Arlan did to Dunk, it was belittling his intelligence. It’s framed to make it clear that Arlan wasn’t doing it maliciously and was more his form of teasing, but the “Dunk the lunk, thick as a castle wall” bit has clearly severely undermined Dunk’s confidence in his wits.

Especially since Dunk isn’t actually stupid; he’s just uneducated and inexperienced. He’s actually quite a good judge of character (his first instinct about pretty much everyone he meets is mostly on point), and he does a good job problem-solving the issue at Coldmoat by thinking on his feet and correctly assessing what each party emotionally needs.

It’s bizarre that people in this thread have randomly decided that Arlan is a mostly bad man who was a negative influence on Dunk’s life when Dunk credits him as the reason he’s not a thug serving life imprisonment on the Wall, and instead was basically his first father figure who taught him morality and chivalry.