I've been italicizing my journal's name on my resume (to show my involvement in its activities). Recently I realized that maybe the journal as an organization, rather than as a journal publication, should not be italicized. Since I'm in the org and not the journal publication itself (except my name on the staff list), should I should keep the journal name plain text (not italics/underline)? It would also make it look consistent with the rest of my education section where all the org names are in plain text.

It doesn't matter. Anyone looking at your resume will spend a maximum of 30 second on it. That isn't enough time to contemplate whether a journal is an organization and if so, should be italicized. Keep it as consistent as possible with the rest of your resume, but really, no one will care.

Not wrong either way, but italicize if you want to draw attention to it.