Religion functions both to challenge and to legitimate particular actions, attitudes and beliefs. Even liberation theologians must legitimate their positions. A canon which does not reflect these needs would not be useful to people. A third problem is that one can never produce a document which everyone will interpret in the same way. Any canon that was produced could be abused and misused.
Interpretation is never a strictly objective process.
One brings presuppositions to the text and reads texts in light of these presuppositions. Reading texts involves dialogue between the reader and the text. There is no such thing as a non-ideological reading of the Bible. Even if someone were to remove problematic passages, people could still read the texts to support their own ideology. A fourth problem is that texts can be oppressive and liberating at the same time.