Reading the end - cheating or not?

A couple of months ago, a friend of mine told me about a complaint her brother had about Dan Brown's The lost Symbol: The book lied to him, making him believe that Langdon is dead. This didn't happen to me, because by the time I reached that section of the book, I had already read the end. 

There seems to be a lot of controversy about reading the end first. Most people yell at me, when I do this, saying that it's cheating. However, the few that do it too (like my friend) find it normal. 

I see reading a book similar to watching an opera. If I know the opera well, I can enjoy the music and the story much more, because I know what it happening, and am not distracted by suspense. When I don't know the opera, I concentrate too much on the development of the story to be able to actually listen to the music properly, and enjoy it. This happened recently, when I was seeing Stiffelio at the Met. Stiffelio is a fairly unknown Verdi opera written shortly before Rigoletto. I had never heart of it before, however, it had been produced by the Met once before, in 1993. The music is gorgeous,  the singers were great, it was a very enjoyable performance. However, I would have to see it again to be able to say more about the music, because I concentrated too much on the development of the story (a weird story about a protestant minister in Austria that had issues with his wife, who got seduced by some slimebag). 

When seeing an opera a second time, or third or fourth .... I notice more and more nuances of the piece, also because every performance and production is different. 

I don't have the patience to read books two times in a row. There are too many books, there is not enough time, it takes much longer to read a book than to see an opera. 

When I am about one third through, I therefore often read the end, so that I can enjoy more of the development of the story, and understand the little hints the lead to the end. And when I finally arrive at the end the old-fashioned way, it feels like I reacquainting myself with an old friend.