I think it's irresponsible if they haven't paid attention to their privacy settings and they have information on there that they wouldn't want their clients to see. (What clients may wish we hadn't seen is a different issue. That's our responsibility if we decide to look. I don't think therapists have a duty to protect clients from themselves outside of the therapy setting if there's something on Facebook that may be uncomfortable for a client to know.)

On the other hand Facebook constantly changing how its privacy settings work is a big pain in the butt, and I would understand if a t had accidentally not kept up to date with it. If I were them I wouldn't post too much. I do think for their own sake therapists have to be a little more careful about managing their public persona than people in some other professions do.

I don't Google my t, but I understand why others may decide they want to. I don't think there's anything unethical about it as long as T has posted something publicly. But I do think you have to evaluate the risk of feeling awkward for having seen something that you become uncomfortable telling your t about later.