I watched the whole thing and what struck me the most was that Belize used to import a lot of chicken meat and the Mennonites made it so they didn't have to. It's almost like there's an objective way to measure contribution.
The Belizians also weren't too upset that the Mennonites liked to "stick to their own" for this very reason: The Mennonites bring a benefit. The interviewer did seem upset about it though. He constantly grilled the various types of Mennonites about how racist they were and why they didn't intermarry. Those that did allow others to become Mennonites still got grilled and the interviewer didn't seem to like that there weren't many nonwhites in the congregation. I suppose he wanted them to outreach more, or change the religion so it attracts a more diverse crowd.