Alan
I didn't make my point very clearly. If you have a traffic-related reason for refusing a clearance, of course you must. That's your job.
But you've described refusing a clearance in circumstances when there is no traffic-related reason for doing so, but rather because you think the pilot might be breaking the law by accepting the clearance. Presumably you think you're doing the pilot a favour and making his flight safer, but there may be reasons (which I was trying to describe in the previous post) why the act of refusing the clearance actually makes the flight less safe. Not unsafe, but less safe. It's not just a matter of convenience. If traffic permits, making the decision as to whether it is safer to take a particular route across the zone, or to take an alternative route, is not your job as a controller -- it cannot be because you do not have the information required to make it. All you can see is the traffic, and your decision to grant or refuse a clearance should be based on the traffic situation, and your workload, nothing else.
I know you work hard to get transiting traffic across the zone -- I witness it every time I call, and I'm most grateful.