American Jews naturally worry about anti-Semitic speech, for the obvious reason that it could lead to anti-Semitic murder, other crimes, job discrimination, and more. They also worry about unfair criticism of Israel, because it could undermine American help for Israel, American trade and professional exchanges with Israel, and the like.
But it seems to me there are also contrary effects. American help for Israel -- especially private help -- is also undermined by any decline in American Jews' emotional connection to Israel, a decline that can stem from (1) growing assimilation, (2) a declining sense that Israel is unfairly embattled, and (3) a declining sense that Jews are unfairly embattled and need Israel as a defender and retreat of last resort. Likewise, what most undermines these days the welfare of the American Jewish community as an independent community (rather than just as individual people)? My sense is that the answer is assimilation and declining sense of common fate, rather than an unwillingness to identify as Jews for fear of ostracism or violent reprisal (a fear that was more serious some decades ago).
Modest amounts of anti-Semitic speech and unfair criticism of Israel, it seems to me, can strengthen American Jews' self-identity as Jews, and thus indirectly support both the preservation of the American Jewish community as a community, and strengthen support for Israel. Feeling embattled as a group tends to strengthen group solidarity. Hearing unfair criticisms for Israel tends to strengthen the sense that Israel is unfairly embattled and deserves more support. Feeling some fear of anti-Semitism reminds American Jews of the value of preserving American Jewish institutions. And it reminds American Jews of the value of protecting Israel, in case one day American Jews may need refuge somewhere just like European Jews once did. ("Home is the place where, when you have to go there, They have to take you in.")
If anti-Semitic speech became too common, these community-strengthening effects may be decreased (for instance, if American Jews became afraid to be publicly identified as Jews) or might be swamped by harmful effects (again, such as violence, ostracism, discrimination, or fear suffered by individual Jews). But my sense is that at modest levels, the existence of this speech in America is a net positive (not an unalloyed positive, but a net positive) both for Israel and for the American Jewish community. And we are talking these days about such modest levels, if one looks at the big picture of Jewish existence in America today.
So far I have tried to be purely descriptive: I have tried to describe what I think is an existing phenomenon, a phenomenon that is positive for Israel and for the American Jewish community as a community. (I should say that I'm a relatively assimilated Jew who doesn't care as much about the American Jewish community as a community as some do; I'm much more concerned with the welfare of individuals, Jewish or not, than with the welfare of the community. Still, even I see some value, so long as anti-Semitism does exist, in America and elsewhere, in protecting Israel and preserving American Jewish institutions.)
Now, though, let me shift to the prescriptive: I think that this phenomenon ought to further strengthen American Jews' support for free speech, including for free speech by anti-Semites and unfair, bigoted critics of Israel. (I think we should support such free speech even without this phenomenon, but I hope this phenomenon strengthens such supprot in others.)
Anti-Semitism, whether Muslim, white nationalist, or otherwise, is out there. Suppressing such speech might diminish anti-Semitism in some ways (for instance, if the suppression is effective and stops the persuasive or attitude-reinforcing effect of such speech), or it might increase anti-Semitism in some ways (for instance, for making the anti-Semites look sympathetic in some people's eyes, or making people who are from the same community as anti-Semites feel embattled and hostile to those who are seen as persecuting them). But on balance, the main effect of such suppression, if it is effective, will be to make American Jews feel more complacent. And publicly identifying and condemning such speech will remind American Jews that there is anti-Semitism out there, that it must be fought -- and that fighting such anti-Semitism and protecting against its most harmful effects is one reason that both Israel and American Jewish institutions need support.
Naturally, there are limits to this. Certainly no-one should foment anti-Semitic speech or conduct, or blow it out of proportion, or tolerate leaving actual anti-Semitic violence unpunished. Increasing group solidarity is not the most important thing.
But if you think that increasing group solidarity is on balance one important thing (either as an end or as a means), the First Amendment rights of American anti-Semites help you rather than hurt you. You shouldn't be demanding speech codes; you should be shipping in more video cameras (and of course demanding protection from violence for those who use them), and publicizing the bad speech that you find.
Free speech is valuable because it informs people -- and it informs people not just when the listener hears and believes the facts the speaker says, but also when the public learns more about the speakers. Publicly visible anti-Semitic advocacy is, at least in America today, an important informational tool: It informs American Jews of the value of Jewish institutions, and it presents this information in an especially emotionally effective way. Again, not in my view the best reason to support free speech, or even close to it. But those who don't share my views about the broader moral and instrumental value of free speech should, I think, consider this more immediate instrumental value.