In economics this is called a barrier to entry. Industries with lower barriers of entry are more competitive (see: restaurants) and have lower margins. Industries high high barriers to entry tend to gravitate towards monopolies. For industries with the highest barriers to entry (like tap water) markets don't work and we have to use heavy handed regulation to avoid letting the industry completely screw over the populace (see: water barons).

Of course it is pretty weird to think of a social network as a utility.