What cities or countries can afford to hold it? How much does WYD typically cost the host city and country?
What Christian youth can afford to attend?
Even if sponsored by parish, which parish can raise the funds?
How many pilgrims from developing countries are there? (Other than pilgrims who are native to the host country, like Brazil in 2013.)
Is WYD another experience of consumption, even if the young adults are living in tents and roughing it? After all, they couldn't have this experience without someone paying for the flight over.
Would there be the same impact of local bishop had such a gathering?
Does World Youth Day promote the cult of the youth, rather than integrating into the into the local Church and holding them to expectations about adulthood?
WYD has its origins with John Paul II, and he was not hesitant about using the papal personality cult. It is the outcome of the centralization of the Patriarchate of Rome combined with the opportunities afforded by cheap energy (though this opportunity is likely reserved only for the fortunate few of the First World, rather than being equally shared by all Roman Catholics).