Chilli
In the situation as you state I agree whole heartedly.
That is where situational awareness comes in - which will of course modify any actions you take....I agree that *normally* pilots should not self-initiate orbits - however I would not go as far as saying NEVER....the pilot is up there and ATC are on the ground - ultimately the pilot has to make the decision - given all the options available if the pilot believes that orbiting is the answer then so be it....I personally would say it is one of the last options I would take...extending legs or departing the circuit completely are the more preferable two...
As a twin pilot in the situation you pose the answer is clear - you orbit. You did allow yourself a reasonable separation for the a/c to land? - exactly - we arent flying in formation here....citation?! In the same circuit as a PA28? whoever mandated that needs their head examined - for a start the citation would be hard pushed to maintain the same circuit pattern...so lets keep it real shall we...Its as bad as putting grob 109s or microlights in the same circuits as pa28/c152 - you have 40kt difference in speed - it causes huge problems for pilots.
The answer is separation.
Anyway in your example clearly the pa28 pilot is wrong as he can and is expected to extend downwind...to orbit in this situation would show a complete lack of situational awareness on the part of the PA28 pilot.
However, extending downwind in the case in question was not an option - back to the orginal post...the pilot is on a base leg...if unsure what to do (i believe we all agree he should have gone to final and executed a go-around) what do you blasting through the final approach track - possibly to the deadside where descending aircraft may be more than a little surprised to you?
Ill give you an example...I was airborne with a student on a direct base approach, I called 'left base to land' and tower said 'WAIT'. This non-standard use of RT left me in an interesting situation - there was a heavy on final approach. Do I proceed to final? or do I HOLD or what?! Apparrently the controller meant 'STANDBY' - which if he had said I would have continued...but the non-standard RT meant I was now unsure where I should be going - particularly if I was being told to hold off....therefore a self-initiated orbit was sensible - it bought vital time to clarify the controllers meaning without the a/c flying into what could have potentially been a conflict situation...due to the nature of the a/d I did not know if another a/c was on final (particularly a heavy) because they would have been talking to a different controller.
As I say...never say never..its all a question of options...