Why just under 2T?
You are correct. Obviously self-handling should be permitted for any size of aircraft where they don't want to be handled.
Signature does handling as low as $25 at the big airports in the USA.
Considering what they give you at that price, it represents very good value for money.
Excessive mandatory handling fees is extremely poor and inappropriate for under 2T class aircraft
Why just under 2T?
The only logical need for "mandatory handling" for GA (anything below a 737) is when there are special airside segregation requirements, which cannot be addressed by other means e.g. a separate GA entrance and apron (we are talking about big airports anyway).
The only customers who actually want handling are ones who are already paying so much they don't care, which is a large section (not 100%) of the bizjet clientele, who pay say €5k-€10k for a flight somewhere, and they expect very nicely presented coffee and croissants when they arrive, with taxis (oops I meant limos) all sorted, hotels booked, etc. That business is essentially what supports ops like Harrods Handling and Signature who charge c. €500 (for a PA28) at Gatwick, Luton, etc.
Obviously airport management doesn't have to allow these firms to operate like that, but for various reasons they do.
GA does have a difficult "corporate image" issue.
Having a network of affordable, accessible aerodromes that bring people convenient access to places. Excessive mandatory handling fees is extremely poor and inappropriate for <2T class aircraft. London City Airport could have been a golden market to capture younger GA affluent fliers, thereby reinvigorating the market, but the short-sightedness of the government, airport authority and local residents have only ensured that it permits limited CAT activity.
Flight schools that actually have a club environment with organized trips and events post PPL - they have planes for training that may be separate from planes co-owned by a group that could be taken away for a couple of days.
Advertising and advertising. You never see a flight school advertisement anywhere. Not even in newspapers or billboards or magazines or TV. So someone who has never known about flying but may be opened to the idea will never see it. I think you only find adverts inside flying magazines!
Taxes. Taxes on training flights is notoriously bad for the industry. There is no sales tax for academic study? Why impose such tax for vocational study like flying?
My aeroclub organizes 1 or 2 foreign fly outs each year, and also a couple of long weekends somewhere in Italy. Anything from 2 to 6 aeroplanes.
We encourage students and new PPLs to come along as pax/2P to build experience and see the opportunities offered by being able to fly yourself somewhere interesting for a holiday.
I went from gliders to a PPL in 1964 - and when renting increased to almost £7 per hour in 1965 I gave up all flying for 21 years. The cost prevents people getting current enough to find out what form of flying they enjoy, so they fly a few times after getting a PPL, then give up. Our newest, low hours, group member would have given up if he hadn't bought a group share before getting his NPPL.
I remember times, when a club organized a trip abroad and it was weeks of preparation. With no internet at all. We ordered trip kits from Bottlang, maps, planned routes, booked hotels from catalogs, send many faxes to airports..... It is so easy today, but you find the old spirit in many clubs, too many dinosaurs are still around. A flight further than the next airfields is major operation - it is not. This is what a plane is for, it is just one means of transportation.
I like the idea of mentoring, but it is one step too far. Many new pilots don't realize, what tool they just got. First action should not assisting someone to plan a trip, it is to show him/her what is possible. One way is trip reports, so thank you for that Peter. I think there are other ways like taking someone with you.
The culture of encouraging should replace the current 'make it complex' culture in many clubs. A few years back, I rented a PA28 from a club. One day I saw a plane advertised and called the vendor. We agreed to meet the next day and I booked the PA28, told them I will go to a farm strip. Everyone came up with some advice. Starting from: "Are you sure you want to go to a farm strip?" "It is dangerous, they are all unlicensed airfields!" "Watch out for cows." and finally "You can cannot land there with a PA28". Now think of a new qualified pilot, would he dare to go? No. It is a well manicured strip with nearly 1000m runway. There are twins based there. Did anyone ask where I wanted to go? No.
I thought this thread was really interesting. Thanks guys.
I reckon it is causing a lot of airports to either give up Customs totally (as in France) or go "Customs PNR Xhrs" where X is gradually increasing.
Customs is still widely available here because Germany is Europe's main transit country for freight so there are Customs offices everywhere for road checks. If it wasn't for that, we'd see the same development as in France.
Maybe the UK will not join Schengen (perhaps Scotland will) but in order to simplify things, the GAR model could be introduced between the UK/Switzerland and the Schengen countries. You should get the massive power of the UK GA lobby to advocate that!
Another positive development in aviation is the acceptance of credit cards almost everywhere. Not too long ago, one had to have a collection of those dreaded fuel cards and it was generally difficult to pay foreign airports. Lately Austria has come up with some ridiculous rule requiring each pilot to appoint a local fiscal representative but that was revoked quickly for GA < 2t.
Schengen is the greatest thing since sliced bread
Yes and No 
I reckon it is causing a lot of airports to either give up Customs totally (as in France) or go "Customs PNR Xhrs" where X is gradually increasing.
Given that the 3 biggest GA arenas in Europe are Germany, UK and France, and the UK is not in Schengen and never will be, this does cause a problem for the UK pilots, and of course for everybody else if they want to visit the UK.
The solution, of course, is a long range aircraft
Which is another thing: if you have a choice between two syndicates, one operating a plane with a 500nm range and the other one with a 1000nm range, and you want to see Europe, go for the latter! It totally transforms the ease of doing it.
I think you are right Peter. One major issue of aviation is the gigantic overhead. Planning the flight, driving to the airfield, getting the aircraft ready, flying somewhere, getting from the airfield to the place where one actually wanted to go, etc.
However, as you say that has improved dramatically thanks to the internet and mobile devices. Not too long ago, a XC trip was a major planning effort, mail ordering maps, putting them on the floor and drawing lines, filling out flight logs, calling airfields or even relying on others for information about flying in foreign countries because it was not widely available.
Now it's almost always a piece of cake. Everything available online and on mobile devices, a flight plan done in 3 minutes, great situational awareness during the flight.
European integration has also come a long way. Today, flying in countries like the Czech Republic or Croatia is just like flying in my home country. In no way it means more stress or requires more preparation. Not too long ago, a German PPL seeking an adventure in a foreign country would fly to Austria...
And of course Schengen is the greatest thing since sliced bread. 
