Not saying them releasing Podesta's emails was bad, just I don't think that's what journalists typically do.
Would anyone have taken them seriously if they just made claims about what were on the emails? You see the same thing going on with the Democrats regarding the summary of the Mueller report: “we don’t believe you, show us the raw data!”
What you have with the Democrats and the Mueller report is that the "journalist" in this case is the Attorney General who was put into the position by the guy the Mueller report is about. As such, it is a case of not trusting the messenger due to bias so they want to see the actual report.
Not sure if anything that happened was illegal (leaning toward no) but they were basically indistinguishable from a campaign arm in 2016.
These are just possible charges, of course. Depending on what Assange knew and when he could have done nothing illegal.