"German" is a nationality and/or race, but "Nazism" was the ideology, and that was the problem. There were Catholic and Lutheran Germans who risked (and gave) all to protect their fellow Germans who happened to be Jewish.
"Islam" is the ideology Muhammad created. "Islamism" is the Western non-Muslim's confused or craven extenuation of what Islam actually is.
The terrorists who rape and behead innocent Christian schoolgirls, slice the breasts off the women of villages who answer "Muslim or Christian?" wrongly, and detonate their underwear ("Fruit of the Boom"?) in worship of Allah are practicing Islam the way Muhammad intended.
Historical, Qur'anic, traditional, mainstream Islam is the problem, and anyone who claims to follow it is one of its agents, whether or not they decapitate their Jewish neighbor, keep prepubescent nine-year-old sex slaves as "wives," or throw dirt into the wide-open mouths of their receptive Hindu dhimmis when they pay jizya.
A more accurate analogy in defense of "moderate" Muslims would be:
Not all Nazis worked the concentration camps.