It shouldn't be banned - however invariably the type of aircraft that flies about at those levels is very slow and quite small, often with unprofessional (in the proper sense of the word) pilots... and usually small enough to avoid paying navigation charges.
I personally believe that in some airspace, navigation charges should be inversely proportional to the aircaft size as the ATCOs workload generated is much higher dealing with these flights than with passenger jets.
These overflights get in the way of everything as they transit!
Cartmans Twin - with regards to your question about passing traffic info - my question to you would be why would you think about not passing it? If you have the time do it - it's entirely sensible and correct that you should. CAS may be a 'known traffic environment', but thats 'known' traffic to you the ATCO, not to the pilots!!