Passage Summary: One critic thinks travel writing is getting worse, but the author argues it's actually just getting harder to impress a public that has already seen everything.

Conclusion: The critic Anderson is being unfairly harsh in his assessment of modern travel writing.

Reasoning: Because the public travels more now than in the past, modern writers face a much harder task in making locations seem fresh, yet the genre continues to thrive.

Analysis: The statement about the public being better traveled serves as a premise that explains why the 'challenge' for modern writers is greater than it was for their predecessors. By establishing that the bar for success has been raised, the author can argue that the continued survival of the genre is a sign of high talent. I identified this as a supporting premise because it provides the necessary context to justify the author's defense of contemporary writers against Anderson's critique.