The following sentence appears in a newspaper:
-My only problem with his noble campaign is that he seems to be speaking selectively about whom should be adopting this wonderful system of government.
Now isn't the use of (whom) wrong here? shouldn't the writer have used (who) instead?
Yes, you're quite right, and the writer is wrong.
The whole clause "who should be adopting..." is the object of the preposition "about". "Who" is the subject in that clause.
It's a fairly common mistake...