Discussing analogies of Israel or Zionists to Nazis, the Chakrabarti Inquiry on antisemitism in the UK Labour Party concluded that such comparisons are "incendiary", "intended to be incendiary", and "bring the Party into disrepute." It thus took the firm and decisive stand that Labour members should ... "resist" saying such things.
I questioned at the time whether the "temptation [is] really that overwhelming." But apparently the answer is yes: for Labour has just overturned the expulsion of yet another "Nazis were really Zionists" member (recall this is what got Ken Livingstone suspended, but not expelled).
Basically, Labour seems to view comparing Israel and/or Zionists to Nazis the way you or I might view a decadent chocolate dessert. Probably not good for you, and certainly not something one should indulge in regularly -- but can anyone blame you if you succumb to temptation every once in awhile?