Ah, I think we are responding to two separate issues. I was referring to Rudin as a mathematical treatment of calculus, in the definition-theorem-proof style, to be contrasted with the more popular and easy heuristic approach. I contend that the Rudin style is a qualitatively better way to learn mathematics. It is also undoubtedly harder to read--but that is because it treats the material in a rigorous, correct way, which is inherently more difficult than heuristics.

Your argument is that Rudin is hard for incidental reasons: he skips steps in his proofs. I personally did not feel this way when I read the book. But I am open to the idea that Rudin is imperfect. I personally admire Rudin's concision, but that may just be my personal aesthetic preference.

My point, and perhaps I did not convey it well, is simply that some subjects (in particular mathematics!) are inherently difficult. And if you want to learn them well, you have to face that difficult head on: you have to read hard books. Euclid's old saying comes to mind: "there is no royal road to mathematics!"