I understand your position, and it does make sense. However, it's absolutely possible to create a bi-lingual country, and is being done in many countries. Here (in Germany), nearly every student learns some basic English, and most learn enough so that they'd survive in an English-speaking country. If every US student would learn Spanish, then the situation would be nicer, I'd think.
Of course they should be able to communicate in English, no doubt. But the fact is some or maybe most can't. Most immigrants, or so I am guessing, are lower class people trying to earn a basic living in the US. It's quite reasonable to say that they didn't even have the chance to learn English where they came from, eg Mexico. Offering them English courses, for free, would be a start - maybe this is done already ...?
But there'll always be people who do not want to learn English, no matter if it's free or not. As someone mentioned before, many never need the English language, as they always live in areas where everyone speaks their respective language. There is just no encouragment for learning the language, it's not necessary to spent time on it.
I'm not trying to argue with anyone, I am not really part of the whole thing anyways - although we have a similar discussion here, which is why I am interested in the topic.
But I just want to encourage you to see it from the immigrants point of view - saying that you'd learn Spanish if you'd move to Mexico is something completely different: you probably had a good education, you're probably white, you're probably a relatively young man, and you've probably got a good income (that is, if you are the average Internet user).
Just some ideas.
Ah, I just saw GL's post ... very nice, I agree nearly completely.