local newspapers are doing such as well. to comment now, one must log-in thru facebook. what was very recently lively exchanges has now turned moribund.
public discussion on such forums has dropped. i used to read the st.louis newspaper's site to get a feel of how the locals felt in the comments section. since such changes the comments have fallen off. possibly as well, so have the page views. i do not frequent that site much any longer. what was a daily "must read" has now morphed into oblivion.
constitutional? probably. good for page views/drawing traffic to the sites...not so great.