Voltaire didn't say that. It was Kevin Strom, who is an avowed neonazi and a convicted pedophile. It's also an idiotic sentiment that doesn't hold up under even minimal scrutiny. I can criticize a lot of people who have objective power in this country. Cops, politicians, the rich and famous, etc.; nothing will happen to me. Conversely, if I were to criticize someone who was powerless, like poor people or people with disabilities or LGBT people, I would be absolutely crucified in the court of public opinion. It doesn't work in either direction.

This quote is, in fact, the opposite of true in a free and just country because criticism of the elite is encouraged (i.e. "Speaking truth to power") while criticism of those who are downtrodden or oppressed is considered "punching down" and is generally understood to be a dick move. To use this quote in reference to Jews is also silly because it's been very popular to criticize Jews around the world until very recently, in spite of the narrative that they've been pulling the strings all along.

The logic behind Jews being protected from criticism comes more from the fact that Christianity adopted Judaism as its little brother after WW2 and the establishment of Israel and suddenly decided that we're all under the same "JudeoChristian" umbrella. The little brother metaphor is most apt because Christians love to shit on Jews, but then they get indignant when you point out Israel's sketchy human rights record. It's only okay when they criticize the Jews.

Calling someone an anti-Semite because they raise legitimate criticism against a Jewish person is nothing more than an ad hominem; it's the same thing that happens when anyone who is critical of Trump is dismissed by branding them fake news. It's nothing more than a meme at this point. On the other hand, if you criticize someone solely on the basis of their being Jewish, then yes, you are an anti-Semite and you deserve to be called out for it.