If the point of journalism is to report in some meaningful way on a subject where it conveys more information to the reader or viewer than they had before receiving the report, then the journalist needs to understand the subject on which they are reporting.
I think that this naturally occurs for journalists working within the same field for many years, but at the same time there are some things that are hard to pickup along the way.
My controversial opinion is that journalism should only be taught as a masters degree that one obtains after having a bachelors degree in another subject. After this the journalist is well equipped to report on fields close to the subject of their bachelors degree.
Then we would potentially get much more competent reporting within all subjects.