I totally agree with this. There are a disproportionate number of posters on mumsnet who won't answer the door or telephone, who aren't interested in engaging with their work colleagues, who have to have a cap on the number of friends they have and who generally have quite a misanthropic view of other people. They live such isolated lives that it can't be good for their mental health.
Clearly people with mental health issues and/or are ND will struggle, but I feel that only engaging with "my little family" is not a healthy outlook on life.
I find that small talk is a good ice breaker - whether it is about the weather, the news, the awful journey to work due to a crash on the motorway etc, etc.
I will add that it took me many years to become comfortable with talking to people so easily, but throughout my working life I have had to talk to people, first in telesales, then as a sales rep, then to negotiate with suppliers. It then becomes second nature.
I also feel that modern technology makes it far easier for people to isolate themselves. Back in the day we had to pick the telephone up if we wanted an immediate response to something urgent.