As a controller, if I was informed that there was a pressurization issue, and a descent request, i would consider that as good as a declaration of emergency. However, just the fact that the pilot has told me he has a pressurization issue, I'm going to really be paying attention to his voice in an effort to assess how he is being affected. If i hear the voice wavering, i would inclined to force the aircraft down. I would also be more wary of a GA pilot than airline.
Should there be an SOP introduced for both parties that mandates a descent in the event an issue with pressurization has been identified? Whether or not the pilot requests it? Morally, at what point do I believe the pilots judgement has been compromised and take action?