I think Droid's cheat system does this dance about as well as any game I've ever seen. You can play it straight. You can play it with a walkthrough. You can play it with relatively minor cheats (like fluffing your money). You can play it with fundamental cheats that do in fact affect gameplay (stat boosts, unlimited gems, etc.). You can apply your brain to the poker, you can let the game play poker for you, or you can cheat your way to instant victory. Basically, you can do anything you want, you can do nothing, or you can do anything in between.
I tend to agree that insisting that players
must play the game with all the grind and progression intact is begging for someone else to write a cheat mod. I also agree with Droid that if all you want is to see porn, go watch porn. There's an entire internet of pirated free porn that doesn't require a single minigame. Go watch it.
But to keep talking about
Love of Magic, here's how it does and doesn't "ruin" a game. The first time I played Book 1, I used the walkthrough with no cheats. I realized about halfway through that I found repeatedly battling my way through Elsewhere tedious; I didn't enjoy the poker strategy nearly as much as I did when the game started. So I played it again, this time giving myself all the money and all the gems.
Because I play
LoM for the story, far more than I do the gameplay or the lewds, this worked really well.
For a while. But...the later stages of Book 1 have a ton of unstructured time, which someone on a normal playthrough would spend building stats (exploring Elsewhere, reading books, training, acquiring money, buying gems, etc.). I already had all the gems and the money (and, as a result, all the stats), so that became a tedious slog, because I'd broken the progression. On a second playthrough, it was more or less worth it. On a first playthrough, I would've been annoyed that about a quarter of the game was essentially time-wasting. In that case, cheating "ruined" the game. Thankfully, I'd already played it without "ruining" it, as I did with Book 2 before going on to do a second, full-cheat runthrough.
Ultimately, I think it's about whether you enjoy the tension of not being sure if you'll win a battle, or not being sure if you'll get to bang the princess, or not being sure you're in the right location during the afternoon stage. If you can't tolerate not knowing, then cheat. If you enjoy that tension but don't want to play something a dozen times to see as many of the elements as possible, then use a walkthrough or a walkthrough mod. If all you care about is the story, and you can be certain that you won't lock yourself out of things, then go ahead and cheat, accepting that you're going to give up much of the intended fun. But a well-designed game has a structure, and shattering that structure is inherently going to damage your potential enjoyment.
In other words: cheating does "ruin" games. Whether or not that's a bad thing depends on the quality of the game. If I could cheat my way out of the mindless dialogue to finally put
Perv and the Potatohead out of its misery, I would. On the other hand, I would never cheat my way through an initial playthrough of
LoM's Book 3.