It's not hard to understand - the Americans deliberately rewarded the worst scum of society so long as they were anti-Hitler.
It's well-documented, and blew up in their faces shortly afterwards. The UK even had it's own little concentration camp full of Leftists in Bad Nenndorf - the stories there genuinely made me laugh, the press tried to smear the commander in charge who publicly came out and started roasting the inmates. Translating to a modern comparison, he basically came out and said "They're all pieces of shit, why do you care? They'd be dead on the street from an overdose or AIDS infection if they weren't here. They're not political prisoners, they're pieces of shit!"
Germany had lost the war, and surprisingly, very few people tried to continue the war. Whereas the UK had no issue employing former Nazi officials, since they had the experience necessary, the USA wanted an ideological victory (as it often does) and pushed for anti-Nazis to be in charge. Anti-Nazi doesn't mean "Democratic", it usually meant "Alcoholic paedophile who ran away rather than serve" whereas Nazi Official, rather than hardcore eugenicist, meant "Good at his job, loyal to his country, wants what's best for his people" - Quislings are usually the worst possible choice, and that's all that German Leftists are - above all-else, they are traitors to their country and are motivated by their own rejection by the civil, and sometimes a little extreme, German society.
My verdict - just scatter poisoned coke baggies near their rallies, that'll handle the problem.