ANDYH52 -
Your posting has me intrigued. I can't recall anybody, "supporter of MAN" or otherwise, who has argued the point of view suggested in your posting. However, to give you the benefit of the doubt, I decided to check back through the thread since its inception to see who you might be referring to. The thread is only around 11 pages in length so the exercise didn't take too long. Aside from myself, I found five other contributors who appear to post from the Manchester area.
EX CARGO CLOWN (Manchester) has contributed a one line posting which addresses an issue wholly unrelated to the argument you raise.
SUZEMAN (MCT) has contributed a posting concerning the display of messages on the thread.
MANFOD (Cheshire) has participated in the discussions. Having re-read his posts, I cannot find any suggestion from him which resonates with your allegation.
BASILBUSH (Manchester) - I invite Basil to correct me if I am misrepresenting him, but reading his posts gives the impression that he is very much in the pro-LHR expansion camp. His postings clearly don't match your description.
BAGSO (UK) - As you see, BAGSO lists his location as 'UK'. However, I'm going to make an educated guess that he is posting from a location in the NW, as his input suggests an affiliation with Manchester. But again, having carefully re-read all his contributions on this thread, I cannot find any message from him which argues the point of view which you suggest. Like myself, he clearly objects to the cost of the LHR proposals (or more specifically, the taxpayer involvement in funding associated works). However, in one posting he actually states that he doesn't oppose LHR expansion on operational grounds. Nowhere has he written that regional airports should operate as the solution for SE-originating passenger demand.
Which just leaves myself:
SHED-ON-A-POLE (Manchester) - Having posted quite prolifically over recent days, I suggest that my views are probably quite clear to most regular readers. However, let me summarise. I oppose LHR R3 on the grounds of COST (but without any operational objection). I specifically object to a forecast taxpayer contribution of £8Bn - £20Bn (dependent on source), money which I argue could be much better deployed directly in the regions which lag the SE by an enormous margin in public infrastructure financing.
Early in the debate I was challenged by another poster (Skipness, IIRC) who suggested that I saw MAN as an alternative to expanding LHR. You may find it enlightening to read post No.56 on this thread which dates from 24.04.2015. That is my reply, in which I make clear that whilst MAN can play an enhanced role in functioning as an intercontinental gateway for those located in or visiting the North, it can in no way serve as an alternative to SE-originating demand. More recently 'Felixflyer' challenged me specifically about journey options for travellers originating in Yorkshire. Again, I made the case that MAN is a decent option for these people, but also highlighted alternatives including the LBA-LHR Shuttle and KLM from LBA, HUY and MME to AMS.
At no stage have I argued that additional capacity isn't required in the SE. On the contrary, I have supported the case for LGW with the proviso that it is privately funded and does not drain the public purse. Further, if you read my postings to Felixflyer, you will find that I've argued that the SE does need to plan for accommodating further growth, especially from the leisure sector which LGW is well placed to address.
So, in summary ANDYH52, I cannot find ANY "Supporter of MAN" (whatever that actually means?) making the argument you allege. It is true that regional airports do have spare capacity, and it is true that they can mobilise this to better serve their own catchment areas. But can you point us to where anybody has argued that no new runway is needed in the SE specifically because regional airports can instead cater for demand originating in the SE?
I look forward to you substantiating your claim for us. Otherwise, you should consider posting an apology. Thanks.