Quote:
You gave the answer that you will find in all textbooks right up to the present
Not true at all! Go to the library and read this book:

G. Rickayzen, Theory of Superconductivity (Interscience Publishers, New York, 1965).

You have to distingiush between rigorous theory and what is taught in high school and the first few years in university. The book by Rickayzen gives a rigorous derivation of the Meissner effects starting from BCS theory.