That would mean you would feel uncomfortable browsing any site, there is nothing that can stop an administrator from browsing through peoples pm conversations in the database or just logging into your account by changing your password or even cracking your password using the information in the database if they wanted to.
I think it is wrong to do any type of snooping on your members 🙂
What about a plugin that does not see the password but logs in, in one click, wouldn't it be good to stop hackers, they hack an account you change details so hackers can't get in. The plugin I'm talking about also has force log out button which is good hacker stopper.
Using something like that to stop hackers or spammers even would be a good use but I could see many administrators/owners using it everyday just to be nose and go through your personal stuff. Personally, if it ever happened to me I would leave the forum for good. Delete all my profile info, change my password, ect.