There was a time not too long ago when being pro-Israel was considered an ideal and not simply a politically expedient position. You, unfortunately, have had to grow up not knowing much else besides Netanyahu, who is a monster. Not all Israeli politicians are like him.
Let's not forget that Bernie Sanders is Jewish, as are many of his current and former Democratic Senate colleagues. Off the top of my head, Carl Levin, Russ Feingold, Charles Shumer, Joe Lieberman, all Jewish, all strong supporters of Israel, and all with major liberal cred (maybe with the exception of Lieberman, who seems like a war monger sometimes). For these men I'm sure being pro-Israel has little to nothing to do with political expediency, and much more to do with deeply held convictions. (Of course there are many non-Jewish politicians who also see support for Israel as a matter of principle and not just convenience.)
Sadly, support for the ideal of Israel has become difficult in the last number of years thanks to Likud and their nonstop media machine, which by all accounts makes Fox News look like Walter Cronkite. I hope someday soon that Likud will go away, and that Israel will take a step back on their illegal encroachments into captured territory. Unfortunately, we saw in the last election that that day isn't going to come in the immediate term. But a bad government doesn't necessarily signify a bad state (we've had some really bad governments, obviously, but I think on the whole the US is a very positive state for the world). In the long game, support for democratic ideals, for human rights, for economic opportunity, all while protecting an entire people that the world has tried to do away with many times, is the right policy.