Obviously most people would prefer a perfect relationship over being single in absolute terms.
The problem is that society has socialised us (and women in particular) to believe that a relationship of whatever quality is always preferable to being single. Its an ingrained attitude that arises from the fact that for many years it was financially imperative for a woman to be dependent on a man. That's no longer automatically the case and in fact in many cases its financially better to be independent, but society hasn't caught up.
The reason why people are often stating the benefits of the single life is partly because there's still a PR job to be done for it. Many people would be happier in a relationship, but plenty would not but don't realise it.
For example:
For women who already have children from a prior relationship, being in a new relationship with someone else poses risks and necessitates compromises and often these compromises are not worth the sacrifice for the woman. Having been conditioned over centuries to believe that a relationship is always the ideal state, it takes a certain strength of mind to recognise that yours and your children's best interests are not necessarily served by being in another relationship. It's therefore good IMHO that people are shouting from the rooftops that one shouldn't automatically assume that coupled = better.
Also, there's lots of things you can do as a single person which its harder to do in a relationship: social, intellectual, sexual, etc. This bears repeating because so often women compromise themselves and their needs and goals to accommodate a man with whom they are in a relationship.
And finally there are some people for whom relationships don't really work -- they're not really cut out for them. And for those people its good that they are able to be optimistic about the single state.
I think everyone realises that its optimal to be in a fantastic relationship with someone who fulfils your every need, fits beautifully with your life, with whom you have the same goals and desperately good sex. The problem is that almost never happens. Sometimes the compromise is worth it, often it is not.
I don't see the propaganda in favour of being single as patronising or insensitive at all: I think its a long overdue attempt to get women to remove their blinkers about the centuries-long brainwashing to which they have been exposed and have an honest conversation with themselves about what really honestly suits them. It doesn't mean that everyone is expected to swear off relationships, it just conditions them to be more discerning about whom they choose.
The more we have this conversation with our daughters, the better.