What you're saying is that you would be fine with Police having the power to haul anyone to the station for an interview if the Police suspect them of witnessing something illegal? This is more ludicrous than I imagined.
There is incredibly good reason we don't allow our Police to simply detain anyone without cause: this power is abused all over the world!
Oh my word. Jeez mate! you still missing my point .... Im not saying the police should be able to detain anyone without a cause.
Detaining a witness because you suspect they may know something and aren't telling you is about as close to holding without cause as you can get.
You quote a portion of the article that deals with the inability of the Police to arrest without cause saying the law is 'a joke' while simultaneously saying you only want to force people who have been convicted by courts for withholding evidence? Make up your mind.
Are you being obtuse or trolling?