> a lot of Americans don't have passports [...] set of people who would be excluded Let's keep it real: The contributors to a global science conference are unl

> a lot of Americans don't have passports [...] set of people who would be excluded Let's keep it real: The contributors to a global science conference are unlikely to be people who don't have passports - and in case that happens, getting passports in the US is as easy as filling in a form and driving down to the local post office. Whereas even getting a business travel visa to the US is a month-long bureaucratic nightmare for 80% of the world's population (basically everyone bar EU, Japan, Korea and AU/NZ/CA).