I'm curious about your "have a negative impact on health" approach. The density of a typical city is orders of magnitude greater than anything that our ancestors have seen in nature; and, historically, cities have been a breeding ground for all kinds of diseases (because sanitation is harder and spreading is easier). Can you clarify what exactly you meant?

I'm not sure that higher pollution is innate in lower densities, or whether that is due to the specific way our suburbs are designed today, and the technologies (such as ICE for transportation) that we use to enable them. It feels like an engineering problem.

And sure, putting everyone into a giant anthill might make it cheaper to contain and dispose of all the generated pollution. But then we should be honest and admit that it's about cost, not about what's best.

Small businesses - I don't think there's any innate value to them, in a sense that we need as many as we need to serve our needs, but there's no "right" for any particular small business to be viable in a world with changing conditions. If suburbs can sustain fewer small businesses, so be it.

Segregation is an orthogonal issue. I think you meant stuff like "white flight", but it is a symptom rather than a cause. If you prevent people from moving away, it will not resolve the tensions that make them desire to move - indeed, it may well exacerbate them.

What you refer to as "modern urbanism" sounds like an ideology that insists that it's the right solution for everyone, and those who disagree should be forced into it for their own good. I think that different people have different preferences in this aspect, as they do in most others, and that any approach should, ideally, try to respect those preferences, rather than ignoring them, or pretending that they are irrelevant.

Walking is good for your health. It's basically impossible to walk anywhere in the suburbs. Many don't even have sidewalks.

In a car oriented suburb where you have to drive to literally every location you have to try extra hard to get even a basic level of exercise.

Again, you're pointing out issues that are about a specific implementation of low-density living, and not inherent to the concept itself. Why can't we have suburbs with sidewalks, for example?

FWIW, the suburb where I live is on the edge of a wilderness area. There are several great walking, cycling and hiking trails within a 2 mile radius. Some of those are fairly steep, too, so even one mile provides a good workout. I find that I engage in these activities far more often than what I lived in a large city, and had to drive for quite a bit before getting anywhere bigger than a tiny block-sized park.

Sure implementation details matter. There's lots of good, traditionally built, well crafted small towns (with sidewalks!) outside of major cities that are "suburbs." Typically when an urbanist is disparaging the suburb they're talking about the common strip mall, cul-de-sac suburb type that isn't this. There's studies that show that these poorly built suburbs discourage walking and negatively affect health. Pick up the book Happy City if you're interested. It discusses how the differences in design of cities has implications on people's lives