I would summarise your points as “I don’t like tourists, so I will make arguments against digital nomads” (which you summarise with your last sentence which is flamebait IMHO).
> $1,200 in tax from 4,000 digital nomads is...$5,000,000.
The export income from nomads spending money earned elsewhere is the total amount they spend less the imports they cost: it is certainly not just the VAT. USD10000 x 4000 is 40 million of export income - that is actually a significant number that politicians would chase after (well, they would here in NZ).
> Thailand's economy generates $500,000,000,000 a year.
Thailand’s export income is ~215 billion (2017), not 500.
> The expat contribution is a tiny, minuscule drop in the bucket.
Irrelevant: you could say about every small export business, so why not close them all?
Economically, look at the marginal benefit of adding one digital nomad, and decide whether the benefits (export income, but also positive externalities) outweigh the costs (negative externalities like social costs of having “bad” foreigners, or “colonialism” etcetera).
The marginal export income from a digital nomad is say USD10000 per annum. That is economically great, so long as the social costs are not too high.
Note that I’m from NZ and I definitely think it would be economically worthwhile to have high income digital nomads come here even if they pay zero income tax (see my cousin comment for that analysis).
Fundamentally: Thailand accepts foreign cockwomble tourists, so I can see little reason not to accept cockwomble “digital nomads” as well.
Edit: I actually empathise with your sentiments: New Zealand gets a lot of tourists (1 in 7 jobs are directly in the tourist industry), and for a long time we allowed foreigners to buy property, so I have seen some of the social damage they do. Albeit the damage from tourists is much less than Thailand from what I have personally seen. Although NZ is more of a “white” country, we still have mixed feeling towards wealthy US people e.g. Theil bought himself a passport here. NZ is more egalitarian than the US, but still has more wealth inequality than the scandy countries (on average most Maori are hit particularly hard).
Edit 2: It’s only really a legal difference between (a) a person that works at home then travels to spend money as a tourist, and (b) a person that works as a digital nomad while a tourist. The distinction is arbitrary. Countries can make whatever rules they like, but if you want tourists, you want digital nomads. NZ gets plenty of backpacker tourists that spend fuck all per day and we welcome them.