I think your non-techie friends are just assuming that the folks that they want to see what they write, will, and those they don't want to see what they write, won't. And, mostly, they're right.
The biggest problem, for me, is that who can see these things is not up to only those involved in the conversation. It hardly even matters what the exact effect is of the rules currently in place, since they could change at any time. The rules on who can see my email inbox don't change. (I think this was what really upset people about Google Buzz: suddenly the rules around who could see what changed, making everyone on gmail who cares about that sort of thing insecure about their own email.)
Thanks but I'm really not that old :)
As to your point, I guess it depends on what your friends use facebook for. As a place for some smalltalk and humor - sure, they probably would never worry if the whole world reads it. But not suitable for discussing anything at all, since you have no control over the audience. And most people don't realize that their inner-circle private discussions are most probably world-readable - I'll save some space and won't list endless possible consequences.
I know a lot of people. I don't have an account on FB. Absolutely zero % of the people I know have stopped talking to me even though 95% of them all have an account.
I trust FB far less than any site online.
Fun Fact: pretty much every other social network, HI5, Tagged, MySpace etc. were all started by spammers. Friendster and FB were just started by douchebags.
The biggest problem, for me, is that who can see these things is not up to only those involved in the conversation. It hardly even matters what the exact effect is of the rules currently in place, since they could change at any time. The rules on who can see my email inbox don't change. (I think this was what really upset people about Google Buzz: suddenly the rules around who could see what changed, making everyone on gmail who cares about that sort of thing insecure about their own email.)