For almost everyone, for almost all of our history as agricultural city-builders, traveling for pleasure has been a small or entirely absent feature of human lives. That's still true, today. Doesn't seem particularly necessary, given that.
Something to aspire to, that everyone can be a tourist more than very, very rarely in their lives? IDK, maybe. But remember that most in the US will pick Vegas or a Mexican all-inclusive beach resort or something like that over anything especially horizon-expanding, and people in the rest of the world probably aren't much different so far as that goes. So unless you're picking the destinations, I wouldn't count on most of a large increase in tourism-related travel to be especially ignorance-diminishing.
It strongly depends on your definition of necessary, and your linking of tourism to the reduction of ignorance.
No individual died from lack of tourism. One neither eats nor breathes tourism.
Yes, it was a large part of the world economy, so it is, or was, necessary to the status quo, and the status quo maintains many a lifestyle rich and poor, so it's specifically necessary to maintain the direction of the world as it was in late 2019.
But necessary like food, water, shelter, and healthcare? No, tourism is not necessary. Tourism is inaccessible to a percentage of the world populace, therefore it's not necessary.
Will governments define "necessary" after this? What mesh of dependence upon keeping their citizens alive will be determined? Will it even be considered in the rush to re-open?
I have a few counterpoints against your first sentence:
0. Tourism isn't a cure for ignorance, but it helps in widening worldview and experiencing how other people live and see. However, today it is mostly about having some time away from your residence/work.
1. Tourists are a small though non-negligible part of humanity as a whole
2. A large part of the people who have traveled as tourists have traveled to tourist spots, places that are developed to cater to the _tourists_ and hence aren't an authentic representation of the local population.
I don't disagree, but I believe that it's not the traveling that's widening horizons, it's the readiness of the traveler to have their horizons expanded. Imho, modern tourism isn't leading people astray, it's giving them what they want. It's a tiny subset that wants something else, maybe we need a different term for them.
Tourism can be educational, it's just destroyed by the modern life behavior e.g. social media addiction. Most people now compete on who has done the most trips in their lives, enjoyed the best cocktail in an exotic beach and posted the most perfect photo from the most iconic touristic destination. But you still can visit destinations to learn their history and blend with locals which no book can teach you.
I've been to DisneyWorld but I don't think that gives me much insight into the lives of ordinary Americans?
I've also lived in Spain and am constantly surprised how ignorant most people are about the country despite having been to far more 'tourist' hot-spots than I have?
Something to aspire to, that everyone can be a tourist more than very, very rarely in their lives? IDK, maybe. But remember that most in the US will pick Vegas or a Mexican all-inclusive beach resort or something like that over anything especially horizon-expanding, and people in the rest of the world probably aren't much different so far as that goes. So unless you're picking the destinations, I wouldn't count on most of a large increase in tourism-related travel to be especially ignorance-diminishing.