tefilla - Why do we still do chazarat hashatz?

This question assumes that the purpose of chazarat hashatz is to allow for those who were unable to say their own shmoneah esrei (assumedly due to Hebrew illiteracy) to fulfill their obligation to pray.

To make a broad and unsubstantiated generalization; in most orthodox minyanim all the people praying know how to read Hebrew and have access to a siddur. If that is the case why do they need to have the chazan repeat the shmoneah esrei?

Lest you counter with "we are concerned for the minority of minyanim where that is not the case" I would refine my question to "if all persons praying are Hebrew literate and have siddurim, may they choose to refrain from the repetition of shmoneah esrei?".

Furthermore I would also contend that many, if not most, minyanim the congregants are not properly following along during the repetition and are failing to answer amen which causes problems of a bracha l'vatalah. So, perhaps removing the repetition would be in order.

Answer

The Shulchan Aruch rules (OC 124:3)

קהל שהתפללו וכולם בקיאים בתפלה, אעפ"כ ירד ש"צ וחוזר להתפלל, כדי לקיים תקנת חכמים
A congregation which prayed and all of them were adept at praying, even so the leader goes back and repeats the prayer [aloud] in order to fulfill the enactment of the sages.

So the Halacha is clear; the question is why? ShmuelBrin correctly pointed out that we do not undo enactments unless we have a bigger and wiser court (cf. Mishna Eduyot 1:5). minhag suggested that the repitition attains a new communal nature which is not present in the original. I'd like to put forward two other reasons:

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  Since at Chazal's time there was appropriately a repetition, they enacted various prayers to be said in its context, notably Kedusha, Aneinu (the addition for a fast day), as well as Birkat Kohanim. If we removed the repetition, then what would we do with these important prayers? (The Tur OC 124 makes this point regarding Kedusha.)

  
  
  


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  As msh210 points out there still exist a small number of people who rely on the repetition for their prayer. ShmuelBrin noted that there is no decree to seek out people who don't know how to pray. I would like to go further: it is forbidden to ask around to see if someone doesn't know how to pray as, especially nowadays, it can be quite embarrassing to admit that. Maintaining the repetition helps those individuals and it reminds us to always be aware of and helpful to those in need of assistance, and to do so in a discreet way. (This can be similar to other enactments of Chazal that ensure that the well-off don't indirectly and unintentionally embarrass other Jews, such as the enactment that a Kohein read the Mikra Bikkurim on behalf of everyone, lest someone be embarassed that they cannot read it (cf. Mishna Bikkurim 3:7))