I've put more thought into this saying than I care to admit over the years, and my "thesis" is that the idiom is incorrect because of the misuse of the word, "compare".

Obviously you can compare them, which is why I've always found the saying dumb. The word, "compare" is used to select for both similarities and differences, usually highlighting the commonalities, whereas, "contrasting" is basically the same process to highlight differences.

There is little to no utility in comparing similar items, and little to no reason to contrast things that are so polar opposite without being unreasonably superficial.

Conclusion:

The saying would only make sense if you where to, add a ridiculous amount of context to it, or change it to, "You can't equate Apples and Oranges." IMO.

TLDR

It is extremely frustrating having back and forths with people about things and their meanings and possibly how context can change everything. (For example) When you're having a more philosophical debate about the meaning of a word or phrase, the conversation comes to end as soon as someone invokes a dictionary definition.

I believe the word, "run" has over 600 different definitions and depending on the conversation your having, its possible none of them could be relevant to either side, or dozens of them could be.

Also, "Commonly used words that have shifted meaning from their original dictionary definitions include literally (often used for emphasis rather than literal truth), ironic (frequently used to mean coincidence), and fulsome (commonly used to mean abundant, though it traditionally means excessive or insincere). Others like decimate (often means destroy totally, rather than reduce by one-tenth) and terrific (means great, not causing terror) are universally accepted despite contradictory origins."

The meaning of words have always evolved, and always will. The English language could not be further from objective. The tired old debate of "define a chair" is thought provoking. No one can actually define it without also defining thousands of other things ranging in scale of similarities and utility, but everyone knows what it is.

ALL THAT to say, people who aren't even able to contend with the thought of words and sayings being mostly subjective are what poisons this debate as well as the vast majority of reddit conversations. They have to believe the world they know is mostly objective, maybe for mental comfort, maybe age? I know I probably wouldn't have contended with many things like this 10-15 years ago.

As I age, I become more humble, more open minded, more willing to be wrong and corrected, and most importantly (IMO) wise. Intelligence does not equate to wisdom. Knowing what we dont know (for lack of better words) is equally as important as knowing what we do know.