CBB coaches are in favor of expansion because they're worried about their job security, now that mid-majors are getting more respect and therefore more tourney spots. The success of George Mason, Wichita St, SIU, etc. over the past few years has added a TON of pressure on coaches from the power conferences, as well as coaches from mid-majors. The pressure to qualify for the Dance is now greater than ever, and for some programs very realistic.
Coaches favor expansion because the collective job security of a head coach has plummeted. Can't say I blame 'em.