I think it's good if it allowed passing in a binary file and an
encoding, but I think it would be crazy if it wouldn't also take a text
file.  After all the primary purpose of a CSV file, edge cases
notwithstanding, is to look like text to the end user in a text editor
(as opposed to Excel spreadsheets, which look like binary gobbledygook
unless opened with Excel).

Are there any use cases for returning bytes strings instead of text
strings?  If so that should probably be another flag.