How is this even a rebuttal? They're both fruit. They both have peel. They both have fiber and citric acid. Out of all of the billions of things in the world, these are the ones which ended up in a phrase about comparing completely different things? Surely a better phrase would have been "comparing typewriters to jellyfish" or something like that. 

I don't generally hear the term as a rebuttal. More of a statement of comparison, maybe more of a way to infer a similarity or a dissimilarity.
 
I like em' both. They are fruit but they are totally different in many ways too. They say tomatoes are actually a fruit but that's another subject I guess.
 
I was looking at videos from the deepest ocean depths the other day and I came away from that thinking, Man, the sheer variety is really still unknown. There are things down there that make their own light and things that can live  on underwater volcano spouts at hundreds of degrees. They are almost boiling but doing just fine down there.But most people think of anything in the ocean as a fish. Some of these things don't look anything like anything else and probably aren't.
 
Look at figs. Now there's a real difference.Not even roundish like apples or oranges. I won't even go there but to say that everything came from one or two things takes a lot of imagination.

This is like comparing Rob Halford and Elton John.
(They're both fruits with appeal.)

craigb
This is like comparing Rob Halford and Elton John.
(They're both fruits with limited appeal.)

Fixed.

The phrase is probably a variant of an earlier phase "compare apples to oysters." The dissimilarity is a lot more obvious in that phrase, but I expect people found it puzzlingly dissimilar and so substituted another fruit. In any event the problem is not just with the foodstuff employed, but with the current and older meaning of the verb to compare. Currently compare is used to describe a critical process of evaluating two options or objects and contains the implication that there are not only similarities to be found but differences. Compare has thus absorbed some of the meaning of the phrase we all know from essay questions: "compare and contrast." But at one time to compare had a meaning of to equate, which explains why one would need "compare and contrast," instead of just "compare." In that sense the statement that you cannot equate apples to oysters or oranges makes good sense. In common use as a rebuttal in debate, it implies imprecisely if poetically, that an argument that would be valid if it were applied to one situation (apples), cannot be used to validate a proposition about another situation (oranges) because it is too dissimilar. Of course you can still require your opponent to specifically show why the particular dissimilarities the phrase implies make the argument invalid.

slartabartfast
The phrase is probably a variant of an earlier phase "compare apples to oysters." The dissimilarity is a lot more obvious in that phrase, but I expect people found it puzzlingly dissimilar and so substituted another fruit. In any event the problem is not just with the foodstuff employed, but with the current and older meaning of the verb to compare. Currently compare is used to describe a critical process of evaluating two options or objects and contains the implication that there are not only similarities to be found but differences. Compare has thus absorbed some of the meaning of the phrase we all know from essay questions: "compare and contrast." But at one time to compare had a meaning of to equate, which explains why one would need "compare and contrast," instead of just "compare." In that sense the statement that you cannot equate apples to oysters or oranges makes good sense. In common use as a rebuttal in debate, it implies imprecisely if poetically, that an argument that would be valid if it were applied to one situation (apples), cannot be used to validate a proposition about another situation (oranges) because it is too dissimilar. Of course you can still require your opponent to specifically show why the particular dissimilarities the phrase implies make the argument invalid.

 
There is no mention of 'becan' in your post. Please leave the forum.

Compare and contrast are like becan and eggs, ya?

Apple's and Orange's...

 
 
 

 
Or this?
 

Usually when I see the phrase used as a rebuttal it is usually when someone attempts to use a comparison that compares things in a way that is not applicable like comparing a quarterback's tackling ability to a degensive safety. Yes, they are both football players but a qb is not expected to tackle.