百思一解
每个人都在寻求认同，在几十亿的人海里。每个人都在寻求答案，在无穷多的可能中。
正文
前不久发了一篇“美国25年的人口结构变化趋势”的短文，引起了网友的兴趣，我们在那篇博文的跟帖里交换了很多看法。很多看法与我相左，但有相当多很有深度和代表性的问题。应网友请求，把我们的讨论和我对移民政策的看法整理一下，和大家分享。无关对错，只是分享不同意见。
因为在“美国25年的人口结构变化趋势”并未太触及移民政策，这里我先简单概括一下我对移民政策的看法：
- 美国需要移民，移民对美国经济的作用不可代替。
- 美国需要合法移民，不是非法移民。
- 非法移民多属于低技能移民，对社会回报低。哪怕合法化以后仍是如此。
- 低工资非法移民劳动力会进一步挤占美国低端就业市场。
- 非法状态无法管理，有很大安全漏洞，也容易繁衍出新的贫民窟。
- 非法移民带来的社会问题，引起的仇恨也会影响合法移民在这个社会的正常生活。
- 因此美国必须要有效的手段降低非法移民，增加合法移民。
- 川普更有魄力和意愿去解决这个问题。
由于网友提出的议题太多（大约有十个左右），不可能一次写完，我会分几次写出来。
先来讨论一个比较尖锐的问题：非法移民是否带来安全问题。
[网友] Undocumented aliens are less likely to commit crime than native-born Americans.
[虎啸山林] 网友引证的数据表明非法移民的犯罪率低于平均犯罪率。这确实可以理解，刚非法进入一个国家，多数人为了避免被当局发现而被遣返，行事会非常小心低调。但问题这些人是否需要合法化。合法化后恐怕就没那么多顾忌了。根据监狱的统计数据，西裔进监狱的概率2倍于白人，更不用说亚裔，不过确实比非裔低：
| Race/Ethnicity | % of US population | % of U.S. incarcerated population | National incarceration rate (per 100,000) |
| 64% | 39% | 450 per 100,000 | |
| Hispanic | 16% | 19% | 831 per 100,000 |
| Black | 13% | 40% | 2,306 per 100,000 |
即便如此，非法移民引进的极端犯罪可并非可以忽略的小事 （http://www.breitbart.com/big-journalism/2015/08/08/illegal-alien-crime-accounts-for-over-30-of-murders-in-some-states/）：
- Between 2008 and 2014, 40% of all murder convictions in Florida were criminal aliens. In New York it was 34% and Arizona 17.8%.
- During those years, criminal aliens accounted for 38% of all murder convictions in the five states of California, Texas, Arizona, Florida and New York, while illegal aliens constitute only 5.6% of the total population in those states.
这五个州38%的谋杀出自非法移民，包括俺住的加州！您说俺不应该担心吗？不管为自己还是我们的后代？
（待续）
The Mythical Connection Between Immigrants and Crime
Wall Street Journal
...numerous studies going back more than a century have shown that immigrants—regardless of nationality or legal status—are less likely than the native population to commit violent crimes or to be incarcerated. A new report from the Immigration Policy Center notes that while the illegal immigrant population in the U.S. more than tripled between 1990 and 2013 to more than 11.2 million, “FBI data indicate that the violent crime rate declined 48%—which included falling rates of aggravated assault, robbery, rape, and murder. Likewise, the property crime rate fell 41%, including declining rates of motor vehicle theft, larceny/robbery, and burglary.”
A separate IPC paper from 2007 explains that this is not a function of well-behaved high-skilled immigrants from India and China offsetting misdeeds of Latin American newcomers. The data show that “for every ethnic group without exception, incarceration rates among young men are lowest for immigrants,” according to the report. “This holds true especially for the Mexicans, Salvadorans, and Guatemalans who make up the bulk of the undocumented population.”
It also holds true in states with large populations of illegal residents. A 2008 report by the Public Policy Institute of California found that immigrants are underrepresented in the prison system. “The incarceration rate for foreign-born adults is 297 per 100,000 in the population, compared [with] 813 per 100,000 for U.S.-born adults,” the study concludes. “The foreign-born, who make up roughly 35% of California’s adult population, constitute 17% of the state prison population.”
High-profile incidents, like the recent arrest of a Mexican national in the horrific shooting death of a young woman in San Francisco, can give the impression that immigrants are more likely to commit violent crimes. But the alleged killer is no more representative of Mexican immigrants than Dylann Roof is representative of white people.
...In a 2005 paper, the Federal Reserve Bank of Chicago reported that more recently arrived immigrants are even less crime-prone than their predecessors. In 1980 the incarceration rate of foreign nationals was about one percentage point below natives. A decade later that had fallen to a little more than a percentage point, and by 2000 it was almost three percentage points lower.
See http://www.wsj.com/articles/the-mythical-connection-between-immigrants-and-crime-1436916798
即便如此，非法移民引進的極端犯罪可並非可以忽略的小事
I am afraid the source of this information is incorrect. An independent fact checking site had reviewed these numbers and explained that these statistics were wrong. Please see: "Tom Tancredo muffs illegal immigrant murder stats." (Tom Tancredo is the author of the report you cited).
(1): Firstly:
The presentation’s author, James Simpson, told us he had emailed Breitbart about Tancredo’s use of his presentation. "(Tancredo) quoted the whole thing incorrectly," Simpson told PunditFact.
(2): And:
Tancredo used the wrong time period. He thought the baseline number was homicide convictions when it was actually all homicides. Most important of all, he took the presentation he relied on at face value and ignored the hard numbers available from the Texas Department of Public Safety.
And while Tancredo might not have known it, the researcher whose work he used himself has questions about the underlying data he used. We have hard data from Texas that refutes the big and estimated numbers Tancredo used. Undocumented immigrants do commit murder, but perhaps only one-fifth as often as Tancredo said.
(3): As a result, the fact checking site concluded:
"We rate the claim False."
See http://www.politifact.com/punditfact/statements/2015/aug/17/tom-tancredo/tancredo-muffs-illegal-immigrant-murder-stats/
P.S.: This is the thing about Breitbart -- it has consistently misquoted information to spin things its way. I would caution you about the reliability of it as a source.