...long-term damage on the US economy? Humanitarian issues aside, what is the real danger in letting illegals flood across our borders?

that would depend on what planet they are from,how long they stayed and where they locate.

Well.. really it all boils down to control... and money.People don't like not having control of who is in their country, and the government doesn't like losing tax revenues on undocumented workers and their taking advantage of public services that the don't help pay for. This can make some social services unavailable for citizens because of the strain it puts on the system.Some people argue that they steal valuable american jobs, but most of them are day laborers or farmworkers because they don't have the paperwork to get a decent job. SOME americans do need these jobs... but a lot of unemployed people are not looking for that kind of work.It is also hard to control a bunch of people that don't know our language well (some speak great), have different cultural values, and are not familiar with our laws.If they are caught and deported, it would seem like a short term problem, but there are always more coming, with no end in sight, so the problem itself is long term, even if the people aren't.