I disagree. It simply said "If I dislike what you say I will not buy your art". And this is a consequence of artists using their fame and public platform to discuss their personal political beliefs.
Why is Streisand's opinion more valuable than mine? Why is Dennis Miller's opinion more important than mine? The answer is that they aren't. But those people have a public platform at their disposal, and they can use it to speak about their personal views and beliefs.
But Streisand is famous because of her musical talent. The minute she uses that fame to express her political views, she is open to boycott.
It is most certainly NOT unamerican. That musicians and actors think their fame lets them speak out about politics is unamerican.
I agree with this.