Particularly because nothing that I've learned since contradicts it.
I was taught exactly the same! Only it was high school civics in the 1960s. I bet there are plenty of people here who would say they were taught the same in their high school civics in the 1950s, and if my parents were still alive I am quite certain they would say they were taught the same in the 1930s! And as I remember, my mother was quite concerned about Obama’s eligibility, and felt he was not eligible because of his non-citizen father, when he was running the first time! (Fortunately she did not live to see what a mess Obama has made of things.)