Our one-sided, no our political leaders one-sided, support for Israel is damned in various outlets, but it often is not really discussed why said support exists. This is equal parts annoying and aggravating, since it suggests some sort of strange mania that we can clearly denounce, but still (helping talking past each other) simply shake our head at in wonder.
I see three factors at work here. One, strong rhetoric is an easy way to show support, especially when the net result in real terms is not that good. When dealing with a sensitive topic, one where many on the other side might not be as emotionally attached to the whole thing (even if they are on some level), this can be a successful tool. Republicans have shown this in recent years. This might also help explain why studies show that even the American people as a whole are against one-sided support of Israel while their elected representatives do just that. Interest group politics and so forth (money counts here too) provides a means for certain groups to be disproportionately effective. If other factors can help such groups, they will thrive even more.
Second, many here have religious, social, governmental (a former Chief Justice of the Supreme Court of Egypt, or Argentina, for that matter, isn't supplying blurbs to books by Laurence Tribe) and other ties in no way akin to other nations. Mix the Holocaust with the site of the origins of our de facto national religion, and duh, you will have deep connections by that alone. Israel also seems like a 21st Century state (its modern creation alone gives it such a feel) while being surrounded by backward sorts and/or nefarious nations like Iran and Iraq. aid ties also are under duress to a degree unlike many others. It's not like England needs special help, right? The likes of African nations might, but again, we are not as emotionally attached to them etc.
Finally, it is very important for us to have an ally in the region, and the latter connections in particular help Israel to be one. This primarily pragmatic interest, however, cannot be viewed in isolation. I might add "of course." By itself, as GG notes referencing George Washington (in a quote with blog-like vitriol), the one-sided nature of our support is simply counterproductive. The "all my eggs in one basket" self-fulfilling prophecy nature of it alone is troublesome. And, the second group of reasons also leads our judgment to be tainted, as is the "one nation against the world" feeling that opposition generally breeds. All the same, our support (in promotion of some suspect neo-colonial ends to some extent) is to some real extent rational, more so than some criticism seems to imply. The "to some" part is telling though.
It is wrong-minded often enough to imply that something is totally irrational, no matter how easy that might be. This does not mean something is right or productive. The current path in not productive; it is actually rather absurd and horrible. Over and over again.