Always on devices are great -- most people, including myself, demand that out any consumer electronics purchase we make these days. What people really don't like is the idea that a choice that you probably would have made anyway has been forced down your throat in a manner that doesn't logically benefit the end user, and provides many possible drawbacks that interfere with your use of the expensive electronics device you bought.
Microsoft needs to very clearly draw a line that connects mandatory always-on to a benefit to the end user that couldn't exist without the restriction. I'll reserve judgment -- but I'm doubtful that they can pull this off. We already know game experiences can be better when we have auto-updating patches, leaderboards, social integration, etc etc. vs. an offline experience.
The argument I can see them trying is something like "developer can design better games when they have a complete data set of what consumers do in their games." That argument will quickly fall flat for 2 reasons: 1) It's speculative and indirect. 2) It's complete bullshit, because developers should already have more than ample data on usage from the 70% of people who are voluntarily connected to extrapolate the whole. Any self-selection bias is likely to be so small as to be irrelevant.