A&B) It's a levy charged for a government service, so of course it's a tax. You mentioned earlier that people who already have travel insurance should be exempt, but taxes don't work like that. For example, in the west, people with no kids to educate don't get income tax offsets, and pay the same amount (or more) of income tax as those who send 10 kids to public schools. Hardly a new thing to charge a levy even though some people won't benefit from it.
C) I get your point on airlines, but collecting money from people arriving isn't a new concept. Many countries with visa on arrivals do it. Thanks to modern technology, other cash currencies, payment cards in any currency, tap snd pay, etc, could be used. Where there's a will, there's a way.