I dont see the concern for this. If someone wants to cheat as they play solitaire then who cares. Conversly, if someone wants to cut up their cards as they play solitaire, then who cares. They can get nother pack of cards.
The problem is temptation.
If it were really so important to me to not get attacked by goblin hordes right now, I'd be far more tempted to take 2 minutes to switch off goblin siege triggers or set sieger cap to zero than faffing about with retiring, starting a daemon adventurer, killing myself, unretiring.
Never understood what's so appealing about a story which ends "and then the daemon king died and we all lived happily ever after" anyhow. And if that's the story you want, why should you be denied it?
The issue is ultimately tied to one big question: is DF a simulator or a game?
If it's a simulator, players are free to mess around with it as much as they like. But if it's a game, there needs to be some form of challenge intrinsic to the game itself.
Of course, in a game as easily modded as DF, the opportunity to cheat is ever-present. But cheating should
feel like cheating. If you want to mod in a playable Bronze Colossus, then that's your choice, but you're clearly not playing the game as it was meant to be played. (Not that I have an issue with modding in general - quite the opposite - but when you play a mod you are essentially playing a game reimagined by the modder, whether they intend it to be a balanced game or simply a mess-around mod.)
If switching over to play as your enemy is left in as an optional part of the game's menu, then it becomes part of the game. If there is an in-game element that removes the challenge unless the player decides
not to use it, this is a sign of poor game design. Therefore there should be some limitation on who the player can switch to (with maybe an option to turn it off if the player prefers to play in "creative mode").
It's the same reason Toady has left out basic amenities such as a quit button. Sure, savescumming is easy enough, but the fact that you need to use an external utility to do so sends a very clear message that you are not
supposed to be playing this way.
Sometimes players take on extra challenges, because DF played safely is far too easy. It is easy to seal yourself into a fort and survive indefinitely. But that's only because the game is still incomplete; the fact that you
can do this is a flaw in the game's current design and should not be regarded as its ultimate vision. There is already a built-in "difficulty setting" based on the hostility of the local environment and presence of nearby enemies; ideally this should be the main determining factor of how hard the game is (with appropriate reward for taking the hard path), not how much the player decides to restrict themselves.