We all naturally have tunnel vision, and apply our experience to everyone else. I can't speak for you, but many people who don't face discrimination naturally don't encounter the obstacles and don't feel negatively toward minorities; they assume that therefore such things don't exist.
But something is missing from our perception, because the evidence is overwhelming. Just consider that a black-skinned person in the U.S., for example, would be insane to assume they face no racism and no risks from it. A woman in IT would be willfully ignorant to think there is no sexism and she faces no threat from it.
* The historical record is overwhelming, and does not need to be recounted.
* Consider that white-skinned males make up ~33% of the U.S. population, yet look at their overwhelming prevalence in tech, business leadership, government, entertainment, and elsewhere - far more than a 1/3 of the people you see are white guys. Probably not coincidentally, it's the group that benefited most from prior centuries of discrimination. If it was a meritocracy, what is the statistical chance that Silicon Valley or the U.S. Senate would turn out to be so overwhelmingly white male? I doubt you believe that their skin color and gender make them superior (and if someone does, then we don't have to argue about where the barriers are); so how else do we explain their overwhelming proportion of success, and the lack of success for so many minorities?
* Surveys show that large numbers have prejudicial views of people of other races, religions, nationalities, etc. Look at the widespread support in Western countries for openly discriminatory leaders, openly discriminatory policies, and similar behavior by many citizens. This includes discrimination by religion (e.g., Muslims), race (e.g., blacks), nationality (immigrants), etc. Many people, even some on HN, claim it's ok to discriminate (to be clear, I don't mean the parent comment), but in the next breath argue that discrimination doesn't exist.
There's a lot of literature that answers your question, explaining what those barriers are and what they look like from other people's perspectives.