This is not what I mean.  The feature that makes anonymous should be the thing that is always used, so that there is no "suspicion" when it is used.  The goal of anonymity is to "melt into the crowd and to be indistinguishable for Joe Sixpack".  It is like an envelope for snail mail.  Everybody uses a closed envelope.  There's no suspicion that you want to be anonymous when you use a closed envelope.  If all letters would be sent in an open envelope, except those that wanted to keep private, they would stand out.  
Another illustration (negative this time), is if you want to be anonymous on the street.  You can put a bag on your head, but you stand out.  As almost all people show their faces, so if you put a bag over your head, you stand out.  Ok, people cannot see who you are, but they can see that you are a guy wanting to hide his face.

You can say it differently: if you are the *only* person using a service that wants to be anonymous, that should still work.  You shouldn't depend on *how many other people* want to be anonymous to get that anonymity without standing out.
For instance, if it became a habit to publish your viewkey systematically on a public web site when you do a monero transaction, then this principle would be harmed in monero too, because those few times that you would like to be anonymous, and not publish your view key, you'd stand out again.  But this is not what happens with the view key.  The view key is usually only used in a very restrained circle if you want to prove something to someone ; not publicly.