Here is a theory of how kids are "spoiled":
1) Parents deny kids stuff the parents could easily provide.
2) Kids quite reasonably complain about this.
3) Parents feel guilty and eventually give in.
4) Parents don't know how to help kids, but do know they are messing up, so buy lots of stuff to try to make up for it.
5) Throughout it all, parents are on the neglectful side.
6) Otherwise, parents act normally.
TCS recommends doing none of these, so of course it doesn't spoil kids. There are other theories of how children are "spoiled", such as "not enough boundaries". That particular one is vague and incoherent. The theory behind it is something like, "If you get some things you want, you'll be really demanding and arrogant, so the solution is to make sure you rarely get anything you want, and then you'll be content". What?
The theory that not hurting kids spoils them, in particular, goes something like this: "Real life hurts kids. Not hurting them will give them unrealistic expectations. It creates an overly nice environment, and they get used to it, and then the real world comes along and they can't handle it."
The idea is to say to your kids, "You will be hurt later. You better get ready for it now. So just hold still while I hurt you." And parents wonder why kids don't listen!
TCS has a better attitude. Life can hurt us, but also we can try to live well and make not being hurt a goal we strive towards. This is known as "the pursuit of happiness" where you try not to be hurt all the time. The other attitude is like making kids sad all the time so when they are sad later they'll don't care anymore. That's not trying to pursue happiness; it's just giving up.
By the way, most objections to the idea of not hurting kids go something like this: if you don't hurt them, something bad will happen, which will hurt them and you.
In other words, they say "if you try a way of not hurting your kids, AND IT FAILS, that will be bad!" Well, duh. We know that. But that shouldn't stop us looking for ways of not hurting anyone that will actually work.