Okay, I'll go along with this. If XC ran to Gatwick it'd be 1 change, the same as it is now :P Although I do appreciate your point: airport pax don't want changes
The lower SWML doesn't have the capacity constraints that the BML has. To me it does look very childish as you seem to be saying that if (I) can't have any, no one else can. What benefit is there to terminating XC at Reading? It doesn't make Brighton services any more beneficial so I don't see any reason why? If anything, surely the Basingstoke - London will have less capacity than Basingstoke - Bournemouth, so if anything XC services to Bournemouth are better than additional Bournemouth - London services?
Taking price out of the equation (by ignoring GatEx) I would change at StP for Thameslink*. As above, I know that airport passengers don't want changes. However, I don't expect the railway to be run purely for my convenience. I think that XC links to Airports is something that is good and should be provided where possible. However, I don't think it should be XC to Airports above anything else.
Its interesting that your argument doesn't seem to be the same for the rest of the airports. XC want to divert their 1tph serving Birmingham Intl away from it via Solihull (doesn't provide any extra links) yet that hasn't got a mention even though keeping this service would be a lot easier than bringing XC back to Gatwick. Why no argument that the XC that currently runs via Solihull to go via Coventry? Why not eliminate the change at Piccadilly and run XC to Manchester Airport? Heathrow only has direct services to Paddington. People seem to manage.
*In reality I probably wouldn't take the train to Gatwick anyway as the people I'd travel with would think that getting any train (changes or not) would be too much hassle
If we want to tempt Gatwick passengers onto the train, I think offering 'Airport advances' and things like that would do a much better job