if it saves lives on the rare occasion that it is used is it worth it?
Of course, if equipment can be useful in a drive to save lives, it ought to find application. However, improperly used and used without proper training, a parachute can be a dangerous device. As you stated, as a D license jumper, you understand what happens if one allows a container to open in the airplane, or a piece of fabric or a pilot chute to get out the door. Failure to protect handles virtually guarantees a fatality...not just for the user, but for everyone on board.
A parachute is a system, not just a passive piece of equipment. It has to be used with proper procedures, and has emergency procedures which must be done properly and in order...and performing the wrong procedure or failure to recognize the proper type of malfunction can turn a salvagable situation into a fatal one very quickly. This is even more crucial in the use of a parachute for emergency operations, especially for those who might elect to use them at low altitudes, or use them in cases when such use isn't warranted.
A good example if improper use are the majority of the Cirrus CAPS deployments...strongly suggesting that pilots have placed themselves in dangerous positions because of the equipment on board. The parachute then becomes a panic button, and is subsequently used under conditions when they ought not. A pilot that elects to fly in weather and loses control deploys a parachute or exits the airplane...he has pushed the "panic button." Unfortunately, he's also elected to make a parachute descent under conditions when one should never make a parachute jump...the parachute has lulled him into making two very bad decisions, either of which could easily be fatal, to say nothing of having abandoned an airplane over a populace which had no choice in his decision making process.
I have yet to make a planned or unplanned descent using one - in the same way that I don't smack my head violently against the tailplane of the Yak whilst wearing a Gentex helmet to make sure I'll be familiar with the experience should I need to jump over the side, or spend a couple of hours bobbing about in a life raft in the North Atlantic to be sure I understand what exposure feels like - I fully expect that should I ever need to use an emergency parachute, it will be a violent, brutally painful experience that will almost certainly result in a couple of broken legs, but that the experience will be preferable to the alternative - frankly, you'd have to be mad to want to use one.
I own two parachute rigs, and far from "mad to use one," I find making a sport jump a highly desirable aeronautical activity, and simply another facet of general aviation. One flies a canopy and one flies one's body in freefall every bit as much as one flies a single engine Cessna, a sailplane, a gyroplane, or a helicopter, using aerodynamic principles and control inputs.
A big difference exists between wearing one's protective helmet, and wearing a parachute system. Your helmet won't deploy in flight and potentially destroy your aircraft and kill you. Your helmet won't experience malfunctions that can kill you. Your helmet is designed to provide limited blunt trauma protection, not blossom into a flying device which you will operate and manipulate completely independent of your aircraft, to fly to a landing position on the ground.
I frequently wear a helmet while executing pilot duties, too...and unlike you, I've had occasion to test mine, and use mine. In fact, on a regular basis, my helmet is used to protect me from injuries during violent maneuvering when my head may strike the aircraft canopy...and it sometimes does, as well as protection provided during ground impact or a crash (which it has also done).
Your helmet does not require frequent inspection and rebuilding. A parachute requires frequent inspection and repacking. Your helmet does not require operation of handles, releases, controls, whereas a parachute system does. Your helmet does not become a flying machine. Your parachute does. Your helmet does not experience life threatening emergencies which require user correction to prevent injury or death. Your parachute system certainly can.
I carry a firearm, and am required to demonstrate proficiency with the firearm, as well as a working knowledge of the principles and legalities of use of force. Several of my employers, including my current one, have required the carriage of rafts and survival equipment on board the equipment. Accordingly, I have been required to undergo training and to demonstrate water survival, while wearing flying clothing, including righting an overturned raft, providing aid to others in the water, survival away from the raft, etc. I have a fire extinguisher on board, and have not only used it on aircraft fires, but have been required to undergo training in the proper use thereof...to include demonstrating putting out a fire using the extinguisher.
I recently underwent recurrent training. Prior to arriving at the company headquarters for classroom and then simulator training, I was required to demonstrate in the airplane a working knowledge of use of all the emergency exits, equipment, etc...right down to physically opening each kind of exit, retrieving and donning emergency equipment (including onboard firefighting gear), and so forth. You see the point. One might take that example to the extreme and ask if we're required to deploy emergency slides or escape reels...the answer is "no." Due to the cost (hundreds of thousands of dollars) involved in blowing all the slides, we don't do that. The slides undergo regular inspections, however, and even the escape reels must undergo regular drop tests with weights, and must be individually maintained and their wear, use and life limits closely monitored. There's a big difference between getting out of an airplane in flight and freefalling clear in an emergency situation and then deploying a canopy to a successful landing, and jumping onto a rubber slide on a stationary aircraft on the ground.
You shouldn't anticipate a violent parachute jump...it's not the jump, nor the opening, that should be your concern. Neither should the landing be a concern. Being able to get out, get stable, or know when you don't have time to get stable, deploy, recognize a malfunction, recognize a good canopy, clear a malfunction, cut away (if applicable), and maneuver and land the canopy around obstacles such as powerlines, etc...these are critical things you should know and understand not only regarding parachutes in general, but for your specific system. The differences between a round parachute and a ram-air parachute, for example, are significant, as are the differences in their control under normal and abnormal conditions...even releasing one's self or collapsing the canopy...crucial of their own accord in the event of a landing under windy conditions or landing in water. Even a landing in water requires specific training; your helmet won't drown you...but your parachute most definitely can.
A parachute is a full aeronautical system, just like your parachute. You check out on a new airplane, and you receive flight instruction and must demonstrate proficiency in learning to fly. The same should absolutely apply to the use of a parachute.