What am I "trusting" Slashdot (or "the readership".. wtf?) with exactly?
You are trusting Slashdot with your username, your password, and the text you submitted in any comments or stories you may have written. If you do not use this username or password anywhere but here, (and good for you on that), then you are making the data you give them less valuable. That's a sensible thing to do, but you do trust them with that.
If you had zero trust in Slashdot, you wouldn't even give them that. They could, if they were malicious, alter your submitted posts to make you out to be a pathological monster vowing to murder a world leader and alert authorities of that country. Those authorities might not believe in the rule of law and send agents after you.
A far fetched example of course, which means you don't have to trust them very much, but it cannot be zero, or you wouldn't give them the little information you did.