Does it not occur to you that procedures are in place for good safety reasons?
Yes, and one of those procedures is evacuating the aircraft on your own. That's why you get the safety presentation that carefully points out all the exits, and how to open doors, and how to put on life vests, and so on. That presentation is there so that you can get out on your own if you have to. If the procedure were simply to wait for commands, the safety presentation would consist solely of a sign saying "do as the crew tells you." The crew is there as emergency safety technicians, not as police officers.
I've always assumed it is so that passengers can assist CC if required in the event of an emergency. eg If one or more CC have been incapacitated.
If the cabin crew requires assistance, it will explain what needs to be done. The instructions are for passengers who must fend for themselves if for some reason the cabin crew is unavailable.
It had never occurred to me until I read your post that some of my fellow passengers might regard it as an invitation to open a door if they consider it necessary. A troubling thought.
You're welcome to wait for instructions from the cabin crew. If the emergency isn't too life-threatening, that's probably a sound policy. But if it's a dire emergency, I'll leave on my own, and you can stay behind if you want. I'll try to watch you through the windows from my safe 100-meter observation position outside the aircraft—that way I can help the emergency services identify your charred remains.
There may be people who will exit for the wrong reasons; there are even FAs who will do this, sometimes. Real-life emergencies rarely take place as smoothly as they do in training courses or safety videos. But I know enough to recognize dire emergencies in most cases. And there's nothing more dangerous than fire aboard an aircraft, so if I think the aircraft is on fire, I'm out.
As for the cabin crew member who initiated the evacuation on her own in the case under discussion, I think it's better to be safe than sorry. Funny smell + no response from FD = possible fire danger = evacuate now. It's easy to criticize in retrospect, but she did what she thought she had to do. Expensive mistakes made in the interest of safety are preferable to loss of life. I'd rather be on her flight than be on a flight where we all die of smoke inhalation while she waits for a signed authorization form from the flight deck.