Being opened up to non-students might very well have been the turning point when the experience using it turned to crap, but it's always worth pointing out that it was nefarious from the get-go.

Zuckerberg: Yeah so if you ever need info about anyone at Harvard
Zuckerberg: Just ask
Zuckerberg: I have over 4,000 emails, pictures, addresses, SNS
[Redacted Friend's Name]: What? How'd you manage that one?
Zuckerberg: People just submitted it.
Zuckerberg: I don't know why.
Zuckerberg: They "trust me"
Zuckerberg: Dumb fucks