The problem with having an ECV modification that allows it to go that fast is like letting loose a small car in a crowd. F=ma, and you've greatly increased the mass in that equation. If your family has to jog to keep up with you (and I know you state you don't use it at WDW) then it can go too fast to be safe. An ECV is used regularly among pedestrians, but is a motorized vehicle. It has to be extra safe in that situation, at all times.
Let's get this really, really clear right now:
I don't *ever* use speed at WDW, because of the people who (we all know too well) are NOT paying attention when they are walking...
I don't *ever* use speed at WDW, because quite often my path (as well as my familys) would be blocked by large groups of pedestrians who have strung out across a walkway.
And I don't *ever* use speed at WDW because it's the rules. Plain and simple. WDW has a rule for everyone's safety that you are not supposed to operate a mobility device at any speed greater than "walking speed". I'm fine with that, and I obey those rules, because I respect Disney's right to set them.
Having said all that, I won't remove my speed mod from my Travelscoot (my Fold & Go has no such speed mod) and I will not apologize for it either, because I shouldn't be artificially constrained from going faster than "walking" speed (which can vary widely depending on the individual, and the circumstance. My former "walking speed" was so fast that my adult daughter had to jog to keep up with me. Your "walking speed" might be faster, or slower. It's as individual as each of us.)
I fully and completely agree that ECVs should be "safe" to use among pedestrians, however, pedestrians at WDW pose a certain level of risk to ECVs and their users as well.
One of the reasons that there are so many ECV/Pedestrian accidents at WDW is NOT speed - it's because it's not just incumbent upon the ECV driver(s) to be aware of pedestrians. Pedestrians have a certain level of responsibility to not walk directly into a moving device, or directly into the path of a moving device.
Both pedestrians and personal mobility device users have the same rights and obligations when it comes to traveling in a public space. A pedestrian who decided to run - at full speed - through a crowded section of WDW could cause havoc and injury; that is not limited to ECVs and their drivers.
I can - and do - drive in a hyper-vigilant state all day, every day when I am at WDW (or anywhere in public), but the fact remains that I have no agency over what a distracted pedestrian does. The very last thing I would ever want to do is inadvertently injure someone because they walked into/in front of me, and I take active measures (such as creating my "safety bubble" with family members, and saying in a loud voice "Excuse me!" if someone appears headed right into my path) to help prevent any possible accidents.
But it shouldn't be solely my job as a mobility device user. Just because someone doesn't require a mobility device does not give them the right to walk directly in front of one, or even walk right into one. The "rules of the road" apply equally to *all* at WDW, not just ECV drivers.
So yeah, I'm sure that part of Disney's reasoning is that if they make those devices move slowly enough, it will eliminate a certain percentage of those type of accidents within the Parks. And it might; I can't begin to guess at how many/what percentage per year that would be, but at the end of the day, it really doesn't matter.
It's Disney's Parks, Disney's rules, and Disney gets to decide - as a vendor for rental mobility devices - what amount of risk vis-a-vis speed vs. pedestrian they are willing to take on. As a full-time mobility device user, I get to decide what device is best fitted to me, and my lifestyle. As long as I operate that device in a safe, responsible manner, and within all applicable rules, regulations, guidelines and laws, it matters not one bit how fast it *can* go - as long as I operate it at a safe speed.
But you have little to fear from me, anyway. I have sadly to had to stable Angus for now, and I am full-time using my Fold & Go wheelchair as my condition continues to deteriorate. So, rest assured, I am no longer a threat to you or anyone at WDW, or anywhere else for that matter.