Strafgesetzbuch Section 86a - Important reason why it exists. Time for the US to wake up.

[Jim Lane]

7. A brief lecture on the First Amendment

Consider two cases:
* A demagogue ranting at a crowd persuades them to storm a jail, overpower a handful of outnumbered LEOs, and seize and execute a despised prisoner. (This is how Joseph Smith, the founder of the LDS Church, actually died.)
* Someone writes a newspaper op-ed denouncing abortion as murder and calling for drastic restrictions on it. An unhinged person reads the op-ed and that's the final straw leading him to bomb a Planned Parenthood clinic.

In each case we have speech, we have criminal violence by someone who agrees with the speaker, and we have a causal connection between them. Should the two cases therefore be treated identically?

The answer, as it has developed in American law over the decades, is No. It has generally seemed reasonable to prohibit the speech in the first case. On the other hand, it has generally been thought that freedom of speech would be too greatly curtailed if "this might lead to violence at some point" were accepted as a sufficient basis for making the speech illegal.

The difference has been given different formulations, such as "a clear and present danger to public order." The general idea is that the danger must be imminent, and not speculative along the lines of "this might happen." Obviously this isn't a bright-line test. There could be a series of intermediate cases between the two I described, with the strength of the justification varying along a continuum, and there would be some where even judges who agree on the test to be applied disagree about whether this case meets it. Still, no one has come up with anything better.

The German law described in the OP wouldn't be a tough case. In the United States it would easily be deemed to go way too far in suppressing speech. If it somehow got to the Supreme Court, there would be a 9-0 decision striking down the law.

My personal belief is that our current First Amendment jurisprudence is, in this respect, fundamentally sound. There are probably quite a few people here who would disagree. I'm not going to bother trying to persuade them. I'm just trying to answer your question about the constitutionality of a law suppressing the use of Nazi (or Confederate) symbols.