I don't know if we are doomed to repeat history, but we certainly are doomed to constantly hear simplistic historical arguments.
Some of these have been flying around lately in regards to whether the US should allow the immigration of refugees from Syria, in the wake of the Paris attacks in which there is some evidence that one of the attackers may have entered Europe via Greece as a refugee. (I think the fears in this regard are mostly ill founded. The majority of the terrorists in the Paris attacks were French or Belgian citizens, and past experience shows that it's much easier to get a terrorist into the US on a student, tourist or business visa than to go through the arduous multi-year process of being allowed to come in as a refugee.) However, these debates don't tend to happen calmly, and so we have on the one hand people making the analogy between Syrian refugees now and the Jewish refugees that the US turned away in the later 1930s, and on the other people arguing that Jewish refugees in the 1930s were nothing like the Middle Eastern refugees today. Here's a section from that latter piece:
The first, and most obvious, difference: There was no international conspiracy of German Jews in the 1930s attempting to carry out daily attacks on civilians on several continents. No self-identifying Jews in the early 20th century were randomly massacring European citizens in magazine offices and concert halls, and there was no “Jewish State” establishing sovereignty over tens of thousands of square miles of territory, and publicly slaughtering anyone who opposed its advance. Among Syrian Muslims, there is. The vast majority of Syrian Muslims are not party to these strains of radicalism and violence, but it would be dangerous to suggest that they do not exist, or that our refugee-resettlement program need not take account of them.
On a related note, the sympathies of Syrian Muslims are more diverse than those of Nazi-era German Jews. A recent Arab Opinion Index poll of 900 Syrian refugees found that one in eight hold a “to some extent”-positive view of the Islamic State (another 4 percent said that they did not know or refused to answer). A non-trivial minority of refugees who support a murderous, metastatic caliphate is a reason for serious concern. No 13 percent of Jews looked favorably upon the Nazi party.
I'm certainly not here to justify turning away Jewish refugees in the 1930s, but I'm not sure that that distinction is as clear cut as the author immediately imagines. From our current vantage point (and keeping in mind the actions we took later in the war) we tend to see World War II as a war in which fascism in Germany, Italy and Japan was pitted against the civilized world. Thus the suggestion that Jewish refugees in the 1930s presented no worries to Americans because there was not some percentage of them who supported the Nazis. However, the contemporary image in the 1930s (like our own situation in the Middle East) was arguably more muddled than that. Communism and fascism were the twin evils of the age, and it wasn't immediately clear which was preferable. Some people sided with one against the other, and others took a "pox on both their houses" approach and wanted the US to remain as isolated from Europe as possible. While for obvious reasons the number of Jewish refugees who were Nazi sympathizers was just about zero, there doubtless were communist sympathizers among the Jewish refugees, and playing up fears of communism was one of the not-obviously-anti-Semitic ways that people justified wanting to keep European refugees out of the US.
Why was it not unreasonable to suspect that there were communist sympathizers among potential Jewish refugees? Well, among other things communists and fascists had been fighting it out in Europe for the last decade, in street fighting, elections, the Spanish Civil War, and starting in 1941 they would do so in WW2 as well. If the Nazis hate you and want to kill you, it might make sense to sympathize with their most obvious ideological opponents, and in the late 1930s that looked like it would be the communists. (The brief alliance between Nazi Germany and Soviet Russia in order to divide up Poland was an ideological shock to both communist and Nazi true believers which took some time to digest, though it provided some brief clarity for conservatives who hated both, as we see with Guy Crouchback at the beginning of Evelyn Waugh's Sword of Honor Trilogy.)
And indeed, some of the major communist spies who gave US secrets to the Soviet Union during the war would prove to be Jewish-Americans (including David Greenglass and the Rosenbergs.) Does this mean that Americans were right to oppose letting Jewish refugees into the US during the late 1930s? Of course not. However, at the time world politics looked a lot more complex than they do with our modern day historical hindsight. In addition to simple distaste for foreigners (of which there was doubtless some) people had actual reasons why they thought that political refugees from Europe would bring additional problems to America.
Similarly, refugees coming out of Syria are coming out of a civil war in which both the Assad regime and ISIS have inflicted horrific suffering on the civilian population. Given that at least some of them doubtless come from areas and ethnicities which have suffered much more from Assad's forces than from ISIS, it's not surprising that some of them have a "to some extent" positive view of the most famous group fighting Assad. Does that necessarily mean those holding somewhat positive views of ISIS are coming here to behead people and stage terrorist attacks? No. But it's worth understanding that being trapped in the middle of war which causes you to flee your home can end up giving you sympathies which we, from our vantage point, find very hard to forgive.
And yes, refugees and other poor immigrants are dangerous.
Why? There are two things that hold us back from misbehavior: our morals and our selfish unwillingness to lose the property and comfort that we have. Someone without property and comfort is now down one of two motivations for good behavior.
Does that mean that people who are wealthy and comfortable never support violent revolution or commit crimes? No. And we see cases of "jihad tourism" where people from comfortable families in the developed world become swept up in the idea of participating in violent jihad and eventually go off to participate. In other times and places, people from secular backgrounds would do this to fight for communism or some other ideology that seemed to give meaning to their lives.
But to have really government toppling chaos, you need not only a destructive ideology but a large number of young men who don't think they have good prospects in life otherwise. The ideology is key. Identifying that the young men fighting for communism, fascism or jihad are often poor men who have a sense of grievance doesn't mean that the ideology which defines their movement isn't key to it, even if the individual fighters may be pretty vague on the ideology itself. But if the ideology can be seen at the virus, the poor and oppressed population is the body weakened enough to succumb to that virus. Both are required to get a really good plague going.
This is why refugee populations, as long as they remain large groups of poor displaced persons, are dangerous. Losing your land, many of your belongings, and perhaps even many of your friends and family leaves you with considerably less to lose. And as such, refugee populations can make prime recruiting grounds for crime and for extremist movements.
The solution to this is not to keep people out, which just puts the problem somewhere else, but to re-root people in a new place where they can again have jobs, homes, friends and family. It's the rebuilding of a stable society which protects against the chaos which often comes with displaced populations. And that ought to be the goal of re-settling refugees: to find them new homes in which they can put down roots and become productive citizens.