Here's his Washington Post column.
http://www.washingtonpost.com/wp-dyn/content/article/2007/10/03/AR2007100302061.html
He's makes very good points. No one's looking for a blanket immunity protecting reporters from having to divulge
any sources. This bill mostly codifies into law that which is already Justice Department policy. As Olsen writes, it simply gives federal judges the authority to ensure that federal prosecutors are following those rules, which have been in place for over 35 years.
I have mixed feelings on this. I think some protections for reporters is necessary, though I'd probably be in favor of a more limited protection than that which seems to be offered by this bill. This bill does not privilege the disclosure of classified material, for example, but I would extend that to any case where the anonymous source probably acted unlawfully. Also, the reporter's testimony should be compelled if it is material to someone else's criminal defense, such as in the Libby case.
While I'm never comfortable with anonymous sources, it's undeniable that they have accomplished some good. For instance, how much would we have learned about the Clinton Administration's excesses if no one could rely on reporters keeping their identities confidential?
Rather than protection for a group of people, I see this more as protection of an activity that is, sometimes, essential to the exercise of a constitutionally protected right.