Any community or ecosystem can withstand some external forces and pressure, but they can still get overwhelmed.
There’s also the difference between a digital immigrant and a digital nomad - the first intends to stay and begins to care about where they are; the second may care but will be gone at a whim.
You are paying taxes to your home country if you're American. If you're from another country and living abroad for enough days per year (depends on the home country), then you won't be paying taxes to your home country.
The place you're working remotely from still gets the benefit of you injecting revenue into their area, and you're not taking local jobs away.
In places which thrive or depend on tourism, working DNs are a blessing. The broke backpackers are less so, as they live on the cheap (which is totally fine for them but offers less to the local community).
Also, DNs are a tiny, tiny percentage of public transport riders in places that have public transportation. Likewise, I don't imagine DNs are using vast amounts of water... especially since we tend to buy bottled water for drinking, and we often don't cook at home (so whoever we are paying for food is getting water however they get it).
As for roads and road maintenance costs, those should be covered in part by vehicle registrations. If we rent a car or a scooter, or we take a taxi, the costs are part of the fare.
Aside from building a local dependency on foreign visitors who splash money around, I don't see much downsides to DNs existing in remote places (assuming of course that they behave like decent humans).
A country typically has a framework that determines whether you are a tax resident based on how long you spend there within some period of time. If you stay long enough to qualify and do not pay the tax the next year, you are in violation. If you work around it by moving between countries to stay just below this limit good for you, but you should be aware you are working around the law and are not a bona fide tourist no matter what you say about benefitting local economy and society and splashing money around.
And no, earning and spending more doesn't absolve you--in fact you are obligated to pay more tax in countries with progressive taxes.
The countries you seem to be talking about are likely having tough times overcoming their preexisting problems with law compliance. Try being a positive change rather than import even more of that "law doesn't apply to me" attitude, especially since it seems like it'd not cause a splash for you.
This is indeed my understanding, and I imagine that most digital nomads are abusing tourism visas.
I'm curious how many digital nomads declare their true intent at immigration. I'd guess it's close to zero.