I have family members, now deceased, who actually fought against the Nazis. But I don't think they did it so that people in the US would have to pay attention to German law sixty years later. I understand why Germany has those laws but I think asking the site not to post things that are forbidden in Germany is asking too much.
Should the site also not post things which would be forbidden in Saudi Arabia? If you're going to have a site that no government anywhere in the world would object to I'm not sure what would be left.
I don't joke about Hitler and I'm not joking when I say that the picture of "Jesus" could also be considered a hate crime. I'm not minimizing the effects of the Nazis in any way but the effect that Christianity has had on the world has, in my opinion, not been a positive one. Can I say the same thing about Islam? I don't know if the post will be approved. How many gay people are tortured to death in Islamic countries? How many women are killed because they happened to have been the victims of sexual assault?
What about China? Google tailors their search results in order to be allowed in China. Is that ethical? Is it necessary?
The point I was trying to make is that while I'm certainly glad that Hitler lost the war, and I am concerned about Aryan gangs, white nationalists, and other racist organizations, I would assume that a post wishing Adolf Hitler happy birthday was made by someone who was trolling and that person probably is enjoying the attention they got for it. I think it's unlikely that Hitler had a happy birthday since he was forced to take his own life over a half century ago.
Whether or not such posts should be considered trolling or political speech, how seriously they should be taken, and whether they should be allowed at all is another question. But it shouldn't have anything to do with what is legal in other countries. That itself is another type of, not fascism, but certainly a restriction of freedom. I think if it were up to me I would not have allowed the post, but maybe I would. I think I do appreciate that the site will allow things that David and the moderators don't condone or agree with and that a lenient reading of the TOS is better than an overly strict one.
Maybe I'm wrong but I don't understand why the posts that are in question seem not to have been reported. If it's about the post wishing Hitler a happy birthday, it seems that this is not against TOS. I think that if a post an unregistered user is approved it probably indicates that it was read and determined not to violate site rules. But you can appeal that by reporting it. I do think you have to be careful because if you misrepresent what you're reporting you lose credibility, annoy the people that manage the site, and probably receive less cooperation and actually achieve the opposite of your goal. If you start talking about monetary damages and things like that you almost force the site to take the opposite view because German law is not valid in the US and a threat or warning that has no validity almost dares the site have contempt for the suggestion.
If you're in Germany and there are things on this site that are illegal there, I believe the onus is on you not to view it.