Oh, I'm not for the immigration bill. But that's one argument for it: Reduce the secret inflow. It would be easier to "secure the border" if the brick-layers and carpenters came up I-35 via Greyhound and only the terrorists walked across the Rio Grande.
But, yeah, there are reasons for opposing amnesty. There's a black market for cheap labor which is caused by wage controls, income redistribution, and regulation. The illegals "solve" the problem. As long as they're illegal, the rules don't apply to them. But if they're legalized, their wages become artificially inflated by law, employers have to pay payroll taxes and do paperwork, and they're demotivated from working by taxpayer-funded handouts--the exact things that created the labor black market in the first place. Solution? Get another batch of illegals from somewhere (presumably the same place). And the drive for amnesty starts over for that batch.
BTW: What's an OBL response? Osama Bin Laden?