You don't want everyone to travel - many people don't have a sense of respect and "light foot" that it takes to travel to foreign places without degrading or damaging them.
Tourists might be annoying but scolds, killjoys, and condescending elitists are far worse.
Not everyone wants to (Openness), or could reasonably do a good job of respecting the host culture and environment (Agreeableness and Conscientiousness).
I, for one, will never vote for making my flights more expensive
For example, say you added a $X / mile flight tax that collected $50 billion dollars in a year. You then take that money and divide it up evenly among all tax payers. Around 200 million people file taxes each year, so that would be a $250 refund to each filer. For people who never fly, that's free money. For people who fly infrequently, they probably break even. People who fly all the time pay a lot more. You reward non-flyers and penalize frequent flyers.
But you're right. We're all selfish. I want you would stop flying because it's bad for the climate but I'm not going to stop because my personal utility from flying is very high.
> [You] "But C also causes B!"
Whataboutism.