The Contact Hypothesis is an idea in social psychology which states that contact between groups also reduces prejudice between those groups. The idea was first outlined by psychologist Gordon W. Allport in his 1954 book The Nature of Prejudice.
Since then, the idea has been used to help psychologists understand what creates problems of animosity between racial groups, and how to potentially solve them. A number of studies have been done purportedly reaffirming the effectiveness of contact theory, leading to some proponents of the theory suggesting that those who hold traditionally right-wing views on things like immigration, diversity, and race, only have those beliefs because they haven’t enough contact with immigrants, or with those of a different race. According to proponents, if they had, they wouldn’t hold those views, and would in fact be pro-immigration, and want to live in a more diverse community.
However, there seems to be a lot of research that goes against contact theory.
The first piece of evidence comes from Greece, where researchers studied the attitudes of local populations after they had experienced a large influx of refugees. Not only did they find that exposure to the refugees produced significant and lasting hostility from the natives, but it also prompted them to support policies which were exclusionary towards refugees. The local population also didn’t come to support a moderate party with some exclusionary parties, rather, they chose to support a far-right party instead, leading the authors to conclude that exposure to the refugees led to increased political support for the far-right.
Similar findings have also been found in the United States with regular immigrants, in particular those coming Spanish speaking countries. One study in particular, published in the journal of political psychology, found that individuals who had routine encounters with immigrants who spoke little or no English, developed anti-immigration sentiments, and also developed a feeling that their culture was being threatened. 
Another study from the National Academy of Sciences conducted an experiment in which the author gathered Spanish-speaking (presumably Hispanic) individuals and inserted them into the daily routines of White Americans. In their findings, the author reported that: “This experiment demonstrates that even very minor demographic change causes strong exclusionary reactions. Developed nations and politically liberal subnational units are expected to experience a politically conservative shift as international migration brings increased intergroup contact.” [Emphasis added] 
These are just some of the few studies demonstrating evidence to the contrary of the prejudice reducing effects of contact theory. Perhaps the most devastating blow to theory, however, is a recent study published in the Cambridge University Press. The authors of this study attempted to verify the findings of a previous meta-analysis which had gathered many intergroup contact studies, and supposedly found that the effect of reducing prejudice was very large. The authors came across some problems in their attempt at replication.
First off, the authors set a list of criteria for each study to meet to ensure that the results from were legitimate. Some of these include; the authors of each study had to randomly assign people to contact (only true experiments), they had to measure intergroup outcomes more than one day after contact, meaning that they needed to find some evidence that the effect wasn’t only present for a very short time, there had to be a no contact control group, and finally the studies had to have actual face-to-face contact.
The original meta-analysis had 515 papers, but by the time the authors had their standards met, they were down to just eight papers. They found that the prejudice reducing effects from these select studies were very weak, with most hovering around zero.
The bottom line is that contact theory is far less credible than people make it seem, and that most of the evidence we have now suggests that trying to put different groups of people together and expecting them to “just get along”, might only make things worse.
 Does Exposure to the Refugee Crisis Make Natives More Hostile?
 Waking Up the Golden Dawn: Does Exposure to the Refugee Crisis Increase Support for Extreme-Right Parties?
 Foreign Language Exposure, Cultural Threat, and Opposition to Immigration
 Causal effect of intergroup contact on exclusionary attitudes
 The Contact Hypothesis Re-Evaluated