That is a sore point, apparently. Many of us have asked for that checkbox not to be "on" at programme start up. It's obviously defaulted in the checked position for a reason - I think we all came to the conclusion that it was in Airnav's interests to have users share their traffic by default because without sharing, this (and other Airnav products) would suffer a dearth of data.
Personally, I think the option should be unchecked by default, but I suppose there will always be arguments for and against, and it won't be changed.
DC