While of course any generalization about immigrants (just like one about citizens) will have it's exceptions, I happen to believe that immigrants are in general, beneficial for the country. The people who come from the poorer countries are in general, the more ambitious, optimistic, adventurous and energetic - that's why they come - the lazy folks are still sitting there.
I don't think we so much need to toughen immigration laws. I think the INS/BCIS or whatever they are calling them these days are largely lazy, disorganized and incompetent (and yes I've had lots of first hand experience with them - stunning, I've never seen anything like it, in any organization, private or public). If they could get some degree of professionalism, organization, semi-modern computer technology, training, etc, etc, in the BCIS and have them be an effective, efficient organization - that would be of great benefit.
Immigration laws have already stiffened, and red tape deepened. In the technology sector and our educational institutions, this has already had a chilling effect. Foreign graduate students make up at least 50% of researchers in technical departments in Universities, and foreign workers at least 50% of researchers in high tech R&D organizations. I am a consultant now, but my last "regular" job in a computational laboratory had 60% foreign born workers in it. The "brain drain" was hurting the foreign countries - taking their best people and bringing them here. If you are a staunch nationalist, you better hope these people keep coming!
While I've had much less direct experience with illegal immigrants coming up from the south, I have had some in a farming town I used to live in, and a lot of the locals there felt threatened by them and seemed to feel they were "dangerous". When I saw them, they just looked like poor people who worked hard in the fields to me. I chatted a little with them, and was never afraid, actually, I liked them better than the locals that despised them so.
As to Bush, he and the GOP are really trying to increase their popularity with the Latino vote, which they've already done successfully, and want to continue on with, it's demographics - that sector of the population is the fastest growing ethnic group, and a politician's job, regardless of party, is to get elected. If you want to do that, you won't try to impose Draconian measures on immigrants from Latin America.
I don't remember ever moaning and groaning about Bush, but I'll take a crack at it if you wnat me to. I think the more immigrants Bush lets in the more voters he gets. He's relied heavily on the "hispanic" vote in my state, and those voters get upset when you start shipping their brothers and sisters back home.