We aren't the super-heroes we like to think we are.
Speak for yourself
I was thinking about this earlier keeping in mind the old fashioned round Army parachutes which I didn't think were steerable.
Then I found this:
How to Steer a Parachute | eHow
Tips & Warnings
Round parachutes are usually not steerable and you have little input on the direction of flight.
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To turn that sized chute I can imagine you would need to pull the "toggles" quite a distance which wouldn't easily be achieved. Hooking it up to the rudder wouldn't give enough throw unless the steering lines were geared.
Interesting question though... I would think it would add complexity that could cause it to all go horribly wrong.
These days the standard SL parachutes are squarish, but I assume you mean the old, round T-10 parachute. There is a steerable version called the MC-1, which has panels removed from the rear of the canopy. This gives 8 knots forward speed and a limited amount of steerability for a very small increase in descent rate. I would say that any level of controllability would serve to limit further risk of death or serious injury. If people get it wrong, so be it, but at least they would have limited options.