Your argument about immigrants and their traits is not utterly without validity. In fact, it's pretty good as far as it goes. However, I'm not sure you grasp all its implications. Some points:

1. If the value of immigration to the US is contingent on its difficulty, what happens if we don't make it difficult enough? Where's the quality control then? What you have provided is an argument for keeping immigration difficult.

1a. With the advances of transportation technology over the centuries, immigration is getting progressively less difficult. It may not be a coincidence that the most successful enthnicities in this country are mostly the least recent (the Chinese are a notable, but only partial, exception.)

1b. Already there are immigrants who've been here for thirty years and never bothered to learn English. They're in dead end jobs, or even on welfare. That's not a good trend.

2. It may well be difficult for the poor to get in, depending on where they start from. But it's all too easy for those funded by an evil Saudi billionaire to get in. This is precisely the opposite of what we want.

3. It's not at all obvious how to keep out the evil geniuses and their henchmen. Even sealing our borders wouldn't work. They'd just come ashore at night by submarine.

4. Since we can't realistically hope to keep them out, it follows that we must watch carefully for them once they're here. That means looking at foreigners with suspicion, based on their ethnicity. It's the Red Scare all over again, but without the poodle skirts and bouyant economy this time. It's unfair to the innocent immigrants, but what's to do?

4a. Besides, it's always been unfair for the immigrants. They have a hard time of it. That's part of what keeps out the riffraff, according to your own argument.

5. The only long term solution I can see is to destroy their power base. Bin Laden and his deep pockets have got to go, and in such a spectacular way as to deter any others with his inclinations.

6. In the meantime, it's live in fear. It sucks, but it's better than getting blown up.