American politics has a ridiculously low tolerance of criticism of Israel, so much so that Sarah Palin got away with saying we shouldn't be allowed to "second-guess" the policies of a foreign nation. It seems like the mainstream tolerates almost no criticism, so what there is comes from looney-tune antisemitism on the far right and ridiculous claims on the left that Israel is exactly like the former South Africa.
The left does have a point when it comes to the occupied West Bank, that Israel has an apartheid policy there. The comparison to Tibet seems pretty valid to me as well - while the West Bank occupation was provoked and Tibet wasn't, at least the Chinese give the petty rights of citizenship in a dictatorship to Tibetans.
Left-wing radio here in the Bay Area had an Israeli activist talking about how we should boycott companies and products involved in the West Bank occupation (more info here). I wouldn't support a broad boycott of everything Israeli or everything Chinese, but a boycott related to their illegal occupations sounds proper and well-targeted, even if it's mostly symbolic.
In related news, Matt Yglesias points to the hissy fit rightwingers threw when Jimmy Carter labeled Israeli politics in the West Bank as "apartheid" and notes that former Israeli prime minister Ehud Barak has just used the same term. It would be helpful if conservatives could stop having the vapors and drop some of their political correctness.