The main problem is that a lot of users aren't aware of the purpose of SHARING DC-based application. It has been designed to share files with users. And not to share files with ONLY SOME users. Hubs are only a mean to allow connecting to these users. The second thing is that neither protocols (neither ADC nor NMDC) nor whole application differenciate between public, private or somewhat other. There's only internet network. So, if users use application/protocol for some special case, it's only his turn to study all documentation (changelogs, forums etc.) and to customize app's settings to its need. So there is really no reason to have DHT defaultly off or to inform user with some special things. The third thing is that it is open source application and users take its own responsibility for using it.
If hubs will ban StrongDC++ due DHT, it's only their problem and I will only be glad that StrongDC++ users won't be in such hubs. StrongDC++ has been designed for sharing with all users, so our users shouldn't go to hubs which are against sharing.
And the last thing, if you don't want to share your files with all people, then turn your client off, delete it from your HDD and go away from sharing world.