Scott3:
There is precedence for this. For example NZ has a Border clearance levy to fund customs. Clearly customs services are for the benefit of New Zealand as a whole, rather than the traveler, but the likes of bag screaming etc wouldn't be needed if they didn't travel, so it is not unresonable that arrivals pay the levy.
That is a pretty narrow way of looking at it. A lot of people travel for business, and even many of those who don't, contribute to export income in various ways. Family separation issues are often overblown in the media but there are also genuine tragedies. People who travel are not just going to lie on a tropical beach somewhere.