The key point is that an aircraft that has requested a Basic service should not expect any traffic information. Or get the impression his flight is being monitored, and therefore reducing his\her lookout.
This however begs the inevitable question, then why should I even bother calling LARS up, getting a squawk? We're always told to do so religiously, but what's the point? Just to provide ATCO with an identity that they can deliver a service to the TS and DS flyers in his zone whilst happily ignoring me crashing to my death from a head on?
No matter how you slice this or interpret this, this is the achilles heel of this system. There seems to be zero need for BS. Either remove it, or upgrade it so BS = TS.