I don't think they were foolishly optimisitic. Society was just literally higher trust back then and various factors have eroded that over the decades in a way they probably wouldn't have predicted.
Society was not higher trust.
The very small, and reasonably tight nit communities that were online were higher trust.
And part of that was because there were far more potential real world consequences because the networks were small enough that even by the time I got online in '93 or so, if I you did something serious I'd be able to find a sysadmin etc. at your school or workplace or one of the few commercial ISPs and get someone to take it on themselves to get personally involved in rectifying the issue.
That doesn't scale very well.
By the time I co-founded my first company - an ISP - in '95, it was already rapidly starting to break down, as more and more people online with only a vague, impersonal commercial relationship to their network providers and who had options that meant consequences were rapidly diminishing.
It’s a double edged sword
Computing changed the scale. The problems were preexisting though.