Why Read Old Thinkers?

Arnold Kling:

Should we approach famous thinkers by digesting distilled versions, or should we study them in the original? … Many great thinkers had some terrible ideas … Many … notoriously lacked clarity. … Much of what I do consists of attempts to contribute to the distillation process.

Tyler Cowen takes both sides, as usual:

I’m for distilling, for reasons Arnold offers, but I’m also for reading the originals. …  Secondary sources … do not capture or understand many of the original insights. … The errors of top thinkers are often more interesting … [They] set our minds racing and … [offer] interesting new questions. … Sometimes the value is in having read common sources … [They help] challenge or reexamine your world view or intellectual ethos. … If you rely on distillation for an inexact science, you will do best at capturing its exact parts.

Honestly, the main reason most people read famous thinkers is to raise their status via affiliation, and to prepare to signal how knowledgeable they are.  And yes reading old thinkers can, like travel, help you explore alien cultures.  But what if you actually wanted to learn about the subjects on which famous old people wrote?

It seems to me that if a famous old thinker were actually the best person to read today on some subject, then humanity just couldn’t be accumulating much insight on that topic.  Either progress there is extremely difficult, or humanity can’t or won’t retain new insights there.  And this famous thinker probably didn’t originate his insights; he or she was likely just the best presenter of much older insights.

Cynicism often seems this way to me.  Finding deep insight in 350 year old sayings by de La Rochefoucauld discourages me, as it suggests either that I will not be able to make much progress on those topics, or that too few will listen for progress to result.  Am I just relearning what hundreds have already relearned century after century, but  were just not able to pass on?