Most multiculturalists tell the truth most of the time. The problem is that their truths are irrelevant or otherwise fallacious, including straw person attacks, especially errors of omission. Other irrelevancies include appeals to origins, novelty, popularity, momentum, and most ad hominem attacks.
Some reasoning errors result from historical causal factors. A causal factor is a factor that changes the probability of thing(s) occurring. The legacy of slavery is a causal factor. It increased probabilities of various African-American behaviors, mainly because without slavery most African-Americans would not be in America. But the legacy of slavery is seldom an ethically important causal factor today. Nearly all of it cannot be undone. A big current legacy of slavery is unethical white guilt, not the sort of legacy multiculturalists mention.
On another side, manorial feudalism was a causal factor. But manorial feudalism cannot be undone and manorial feudalism is not coming back. Manorial feudalism is ethically unimportant now.
Multitudes of currently unimportant factors changed history. Everything from super volcanos to the acts of powerful individuals. In general, historical causal factors are seldom ethically important today, except when used in studies to make prescriptions, explain current actions, and predict future actions.
Other historical factors, the MAOA gene variants, for example, are with us today and their frequencies can and should be changed. They are very, very important.
In addition to irrelevancies, the other major category of "true fallacy," is the small sample fallacy. Mass media and cultural Marxian wars against whites sometimes rely on small sample fallacies, often cases of police attacks on African-Americans. But nonmulticulturalists know the reality that African-Americans are dozens of times more likely to commit stranger-on-stranger, interracial assaults. And those assaults will rise exponentially as whites become weaker and less numerous, with massive support from Muslims, Asians, and Hispanics.
In mass media and cultural Marxism:
1. It's true that small sample fallacy X happened.
2. Therefore white guilt and holy war against whites.
3. Mass destruction and anti-white genocide.
Every establishment political ideology is cover for rent seeking.
Other types of true fallacies include circular claims, misleading stats, and unrepresentative sampling.
Sometimes multiculturalists make good points, but then try to use the good points to support atrocious conclusions, often because they know almost nothing about alternative prescriptions. No matter the situation, they see more establishmentism and cultural Marxism as solutions. The fixation on prescribing more wrongs as solutions is a feature of all types of totalitarianism. Their straw person attacks also often result from the fact they know almost nothing about the alternative right and other political alternatives.
When multiculturalists make outright false claims, multiculturalists still think they are telling the truth, primarily because humans tend to believe the truth is what they hear first and most often. And multiculturalists dominate nearly all the mass media. Groupthink, avoidance of ostracization, and absence of cognitive dissonance add to the likelihoods of telling falsehoods.