True, but DNs often pay a premium for many services which locals do not pay. And DNs often spend a lot more than locals do just by virtue of having more to spend.
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).