That's the whole point. Terrorist. Traitor. Coward. Jedi.
It's all about word association. The same way Republicans have (right or wrong) become virtually synonymous with racism and Catholic priests with pedophilia. And Bariss wasn't the first Jedi to go bad and cause some harm in this war by a long sight (hell, we saw another one earlier this very season). Count Dooku of course is the most visible example of that. The public doesn't have a clue he's a Sith Lord (if they even remember what a Sith Lord is at all) - from their point of view, the Jedi
started this war. One bad apple, okay. One bad apple after another after another after another
, very publicly messing things up - and this last one a teenage girl
- and eventually the whole bunch comes under question.
And the best part is, Palpatine doesn't have to make any of it up. The Jedi make it so easy for him.