This is also a serious downside with FaceTime or Skype on a mobile. You are always looking down at the device and that is seldom a flattering look, double chins etc. I have heard this from numerous people as a reason they don't like video calls.
Not to mention the reverse: with video, all of a sudden, I have to care how I look, what I'm wearing, what's visible in the background, etc. Gah, what a pain.
So while there are definitely positive aspects to video calls, and it's great that they're an option, no way should they be the default, either technically (the default state of the app) or "societally" (i.e., what people expect, with audio-only being taken as a sign of something suspicious).
One reason I don't use Google hangouts more often is simply that: it defaults to video, and requires specific action to turn that off. Don't do that shit.