I can buy that argument to only a very small extent. Let's say there will never (in our lifetimes) be a flight from a UK regional airport to Timbuktu - and let's say there isn't even a 737-load of people wanting to go there from London - is it really OK to make a massive hub out of Heathrow just so that a number of people in the UK can fly there non-stop? If we had the 737-load it could use STN for the benefit of London people.
A hub is useful to Londoners but comes at a massive cost of investment and pollution. The price is too high. Londoners wanting to go to Timbuktu can take an indirect flight just as everyone else in the UK needs to.