I can't believe and don't believe that they had trouble with the idea of millions of Jews living in this part of the Middle East. While I wouldn't have supported this stupid idea 70 years ago, the ship has sailed and it would be no more just to kick out the modern Jewish citizens than it would be to kick out all the non-Native Americans from North America.
I assume the people having trouble with the "Pro-Israel" phrase don't want to remove the Jews, but rather would merge the Jewish and Palestinian populations in Israel and the occupied territories (plus the Palestinian Diaspora) into a single country, the so-called "one-state-solution". This might be showing my personal opinion somewhat to say that my first reaction on hearing this solution several years ago was, "that's the stupidest thing I've ever heard." I haven't changed my opinion. Take two peoples who hate each other and leave it unclear who's going to be politically dominant. Just brilliant.
So I don't support that idea and don't think J-Street needs to either. I could call myself pro-Israel, in the same sense that I'm pro-Jordan and pro-Bhutan, and pro-world-in-general. That attitude probably puts me on the far left of the extremely narrow range of political discourse in the US over Israel. It might take me out of the target group for J-Street, which is looking for people who are especially pro-Israel. I think it's fine to be especially pro-Israel so long as that doesn't translate into harming other countries and peoples, and people with Matt Yglesias' attitude can help improve the discourse in the US, to help peace and to help Israel.