I have a FB account, but I don't use it. My wife does. I had to ask her about the privacy settings.
In the same article (link in the OP), there's a reference to 10 things you can't be asked at a job interview; I humbly submit that you can legally refuse to provide your Facebook password based on the following legal limitations:
Employers can't ask about race.
Can't ask about sexual preference.
Can't ask about pregnancy or planned pregnancies.
Can't ask about rehab, medical conditions, mental illness, or disabilities.
Can't ask about religious preferences.
Can't ask about age.
Can't ask about worker's comp claims.
Since your Facebook profile could possibly answer any or even all of these, you legally have the option to refuse to provide your password. Since job applications legally ask about criminal records, using the excuse that they're looking at your Facebook page for indications of illegal activity is extremely weak.
Frankly, any question aimed at an individual's personal attributes, orientation,
or personal background is not only off limits, but illegal. That said, the following guidelines are given by legal advice website Find Law:
If you are asked an illegal question, what are your options?
Let the interviewer know that the question was illegal
It can be tactfully done. If it puts your interviewer on alert, so be it. You can thank your lucky stars that you found out right away that the company is still in the dark ages.
Answer it
If you can honestly give the answer they are looking for, you could consider answering the question. If the question is blatantly illegal, you can lie, too. What are they going to do, fire you for not letting them violate your civil rights?
Raise Cain
Contact your local federal
Equal Employment Opportunity office and file a claim.
http://employment.findlaw.com/hiring-process/illegal-job-interview-questions.html