"If an economy is booming in an area, and people keep trying to move there, that's a sign that the metro is doing something right, and that it's desirable.
"

The latter is true, the former is not necessarily. It's like saying "if a company succeeds, they are doing something right". It's never that simple, and lots of things that are not controlled by the company or city (we'll just sum them all up as "luck") play a serious factor.

"Forcing the government to get in the way and tell people not to go where they want to go is stupid and exclusionary. It's "I'm in, now shut the gates on everyone else".

Again, the former is false, the latter is true.
You have this backwards - the governments aren't telling anyone anything. They are trying to maintain what they have, at a scale they can do. They are being forced to scale in ways they don't want and don't think they can make work instead.

Keep in mind your latter is applicable to other situations as well. "US/China/etc got big by horribly abusing the environment, but nobody else should be allowed to do it".
They are in, now shut the gates on everyone else is literally true there.
Nobody argues this is the wrong answer, which is the point. Shutting the gates, often portrayed negatively in this situation, is not necessarily the wrong answer to situations at all!

Beyond that, framing it this way is just odd. Managing and keeping a place of 10,000 in working order, and effectively serving the population, is not at all the same as 100,000. It's not 10 times harder, it's 100 times harder.

Why should cities be forced to do it, just because of the preferences, mainly of people who do not live there now?
Why do they have to value future potential citizens over current ones?

The rest of your claims feel like a lack of perspective and judging others. It's a portraying of things as only two possible extremes, and saying one extreme (the denser one) is good.
I'm actually suggesting cities and their citizens should decide how far and how fast they want to grow, based on what they want out of life. This will lead to some dense places, some not.

Yes, that means less freedom for people who don't live somewhere to choose to live somewhere. It often means higher housing prices for people who don't already live somewhere to live somewhere. The cost for people already in a given place reaches equilibrium on its own.

It usually trades those things for the happiness of people already there. You can do this if you want, but pretending it's the "obvious right thing to do" makes no sense, and forcing cities to do it, even less.

It also assumes all the things you want succeed at their objectives, which is really rare. Complex systems like this are never that easy to get to behave how you want.

It doesn't at all mean it's harder for businesses to grow (that's just silly), and the suburban sprawl is also sort of silly - there are lots of dense, environment destroying places. It's also orthogonal - you have the same problem either way, because realistically, densifying only works to a point anyway. If you make somewhere 5x as dense, and 5x the people go there, now what?
You think you won't end up with the same problems, but with 5x the population?

(As i argue, you will actually end up with 20-100x the problem, and 5x the population)

People have always found ways to be more consumptive, no matter what the density.
The faith that density is a solution to overconsumption, under the assumption you will be more efficient in a dense environment (and won't increase the consumption) seems highly misplaced.

I would wager if we really get to the density some folks want, we are pretty screwed as a planet. We will make all of the problems much harder than they are now, and have less will and ability to solve them.

In practice - population growth is the thing that drives housing prices, and the environmental issues you cite.

Raising housing prices lower population growth, and vice versa. See, e.g.:

https://www.cambridge.org/core/journals/journal-of-demograph...

You can see for every 1% of population growth, housing prices go up 1.4%

Notably, it turns out this is true even in dense places, so it's not just "they aren't densifying".

I can cite you similar papers showing the raising housing prices lowers population growth.

You want slower population growth, not higher, if you want to solve environmental issues, most of which stem from having too many people.

In practice, the raising house prices, while painful for freedom to live, helps ensure a sane equilibrium for the cities and the population. There is always pain in that, no matter what you do. Destroying that equilibrium seems unlikely to have the only-positive effects that folks seem to think. We already know this is true of almost all other things in nature (IE destroying the annoying mosquitoes would be bad), and i'm totally stymied why people think it will not happen here.

So there you go, this is why "indulging in NIMBY attitudes" as you call it can be helpful and productive, even if you ignore the actual "happiness of people" issue that pervades the debate.
In the end, i'd urge you to see that not everyone who thinks forced densification is a bad thing is an idiot, or doesn't understand the costs/benefits.
They may just think you are wrong whether it's going to succeed or be worth it.