This is a great and very necessary piece. As a lifelong leftist (and a leftwing Zionist), I would add one further category to your red-flag list: borderline obsession with Israeli affairs. I recall as far back as my days as an intern at The Nation magazine at 19 (today I’m 52) some of my colleagues demonstrating such intensive and impassioned opposition to Israel that it overshadowed or at least surpassed all other commitments. When every negative tributary seems to lead back to Israel, there’s a serious problem.