I do not see how you can, realistically or practically introduce charges for those who "do not bother to lose weight", or remove treatment. Cannot be done.
And the same applies to applying a levy to unhealthy foods. Who makes the decisions about what foods are unhealthy anyway?
I do agree with the OP regarding the cause in the increase of type 2 diabetes though. There is a wider range of factors than just obesity and lack of exercise, but those factors themselves are probably the most important contributors.
http://www.nhs.uk/Conditions/Diabetes-type2/Pages/Causes.aspx
AoG said something to the effect that one of the main reasons that diabetes 2 appears to be explosively rising is because we were unable to diagnose it so well previously - I would be very interested to know where they got that information from, because that is certainly not my experience, nor the experience of any health professional colleagues that I am aware of.
What is required, boring as it sounds, is greater efforts in educating the public on what constitutes healthy eating, urging the public to take greater exercise, and the consequences of living a life with diabetes type 2.
A greater focus at school on food and diet and cooking healthily would not go amiss either. Continuing to pressure food manufacturers to remove excessive quantities of sugar and salt and fat from their products should also remain.