Inspired by one of Spender's comments in another thread here, I think this is a good topic for discussion in its own right.
Basically, Spender committed (in some folks' eyes) the cardinal sin of calling *all* model trains "toys". Well, I'd like both to suggest he's right, as well as suggesting the error of his ways.
Wait a minute--how can I have it both ways? Can I have my cake and eat it too?
Yes. So far as agreeing with him, that all models, regardless of how expensive or exquisite they may be, are toys, this is what I call the "man from Mars" view. Supposing a group of aliens were to land among us and study us; they would inevitably categorize our activities and possessions in various ways. One of the top-level divisions would be between things that are essential for life--food, water, shelter, clothing, medical care--and those that aren't. Model trains clearly fall into this latter category; hence, they are toys, in the most generic sense of the word. They're solely for amusement, for enjoyment. (The only people for whom this isn't true are the pushers--the dealers we buy our stuff from.)
But Spender really ought to be more careful around here, in this den of railroad modelers. Because despite the truth of the matter explained above, there clearly are distinctions to be made between the more obvious "toys" on the one hand (like tinplate, including a lot of the offerings in O scale), and what are rather mysteriously called "scale models" on the other hand, meaning anything that aspires to a higher level of realism or fidelity to the prototype.
Not that there's anything wrong with the "toys" (meaning the more toy-like models). To illustrate: I visited the California State Railroad Museum last week, and of course went upstairs to see the models. There are several displays and layouts in various scales. One of the largest is a beautifully-done O scale pike, probably larger than the average size dining room in an American McMansion.
So far from being realistic looking, this was done to perfection with all the stuff one gets from (I'm guessing) Lionel and MTH; the "grass" that looks like green fabric; the buildings that look like, well, plastic buildings. But the overall effect was quite enchanting, and one could certainly see how kids, especially, could be transported to a different world entirely if they were lucky enough to own such a "pike". Certainly not the kind of layout I'd ever build (or buy, even if I could), but one with its own qualities nonetheless.
So there really is enough to go around in this hobby, from the most anal rivet-counter to those who love to just play with toys.