You might be vastly overestimating the correctness of files being imported. Some coworkers of mine have to deal with CSV/TSV imports from enterprise customers,

You might be vastly overestimating the correctness of files being imported. Some coworkers of mine have to deal with CSV/TSV imports from enterprise customers, and the amount of clearly broken scripts is pretty bad. That excel import preview dialog helps non-programmers try to fix these issues beforehand. If that wasn't there, it'd likely be impossible for these people to know where to begin trying to fix the import.