To an extent, some degree of player restraint is necessary. Playing through the game in the correct order is as important as it is with films and books, even in something as narratively hollow as Super Mario Bros. But the difference is, you can’t get stuck on a bit of a film or on a page of a book. Nintendo declareditself as “the supreme arch-nemesis of cheats” (paraphrasing here) saying, in their lawsuit against Lewis Galoob’s Game Genie device, that cheats substantially shorten a game’s life span. We call shenanigans here; nothing makes us lose interest faster than an annoying bit we can’t beat. Indeed, we reckon that a toggle-able invincibility cheat would prolong the longevity of most games; so how about it, eh, developers? Scared of letting us see the ending? We’re not paying you by the quarter any more.
Which sums it up nicely; we’ve paid for the entire game in one fat lump sum, so the game should be ours to do as we like. Locking up 95% of the game’s content seems a pretty odious thing to do after you’ve shelled out full price - imagine buying a tumble dryer, and finding out you couldn’t put your jeans in until you’d put your socks on spin dry 47 times. Perhaps developers are worried that players will just whack the cheat on and cruise to the end, but that’s where individual responsibility comes into play. If some bozo wants to play a side-scrolling shooter where you can’t die from start to finish, that’s their prerogative.