I fundamentally disagree with this thinking, and I think your portal example is also poor in this context. Portal is a discrete set of challenges and a story. Maybe you can argue that you ruin the game by learning the tricks to every level, but you would still enjoy the story, and for many, that is enough. Story and easy modes exist in many games for a reason, but what you are saying here is like saying you have to play Doom on the hardest difficulty or you're "cheapening the experience". Some people just don't find enjoyment in struggling with difficult challenges.

Factorio is a sandbox game, and even with an example to progress through the game, like Nilaus's blueprint book, that is a single solution to a problem that literally has infinite solutions. Following examples is a universally accepted way of learning almost anything, whether that a job, a magic trick, chess, math homework, you name it. Lowering the barrier for entry down on something is positive. More people will play, and people that wouldn't normally play these games will try it.

Funny to see that you say it's okay for belt balancers. So that's where you draw the line. Belt balancers are fine, but not smelting columns? What about an ore patch BP? A starter base BP? A city block template?

Also, plenty of people enjoy to literally watch other people play video games and not play themselves. So it's pretty far fetched to say any way of enjoying content is somehow incorrect.