This is the problem: college students are terrible programmers. There aren't enough consequences for writing bad code in college. In industry, you learn very quickly that everything you learned in college is minuscule compared to what you actually need to know to work. I knew guys who only studied databases or only studied HTML+JavaScript+CSS. And we all expected that this level of specialization was common and even…
Some people are just really good. And a startup makes them even better, and much faster than if they had decided to be "apprentices" or "interns" forever.
The thing about Diaspora is that UNLIKE Facebook or many other startups, its source code is on the internet for all to see. Do you think the original Facebook (written in PHP) didn't have security holes that would be transparent upon reading the source code? For that matter, do you think today's Facebook source would withstand attack if posted on the internet tomorrow?
The question answers itself.
If it achieves its potential, Diaspora will be hardened to a considerable extent because of the scrutiny that open source provides. This is not the time to slam these kids as wet behind the ears undergrads. Their code is pretty good for something written in 3 months. And if you really are that much wiser than them, they are accepting patches.