I think cheating is the wrong word. Unless you are trying to claim some sort of game playing superiority, or get through the game in a shorter time than someone else, or there is some other competetive element then it isn't cheating. The only thing using walkthroughs does is diminish the sense of accomplishment when you finish the game.
Using a walkthrough to get a trophy or achievement seems like rather a hollow victory since you didn't get it through your own skill and intelligence. Having it sit there on your online profile is a constant reminder to you that you were incapable of reaching the heights of achiement on your own. It's also cheating if someone says "wow, you actually got that?" and you sit their letting them think you achieved all by yourself.
But how is using a walkthrough different to asking a friend how to get past a certain stage, or find all of the secret areas, or whatever, when that friend has played the game before you?
No, in general using walkthroughs is not cheating.
“The fundamental cause of the trouble is that in the modern world the stupid are cocksure while the intelligent are full of doubt.” - Bertrand Russell
"When the power of love overcomes the love of power, the world will know peace."
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