I don't think it matters where I am from.
I travel regularly and happen to like flying through Heathrow. So, why should I not wish for it to be expanded just because I am from the North West of England.
If Manchester was the alternative to Heathrow, which as we know is operating at full capacity, then the Airlines would already be at Manchester or any other UK Regional Airport.
United could easily have added UK capacity by adding Flights from Manchester to Chicago, Houston and San Francisco but they have not. After all, they no longer have a UK feed to their Heathrow routes. A deal with Flybe at Manchester would be perfect.
Delta/Virgin could have added Manchester to Detroit, Minneapolis St Paul or Los Angeles and American could have added Manchester to Charlotte, Dallas or Miami, but neither have!