I know that none of us are going to make you change your mind on this, and that's fine. You keep mentioning that signing the waiver would subject you to unnecessary risk. What risk is that? Is it the risk that you'll wreck the car and then have to pay for the damage? If so, I don't see that as being either undue or unnecessary. Should Tesla, or their insurance carrier, bare the risk of your actions? Frankly, I'm glad to see that Tesla is protecting themselves; one horrible accident during a test drive could be very expensive for them and, because the company itself owns the vehicles and runs the test drive, such a thing could impact the company as a whole. I sincerely hope that Tesla does not allow you (or me, or anyone) to test drive without first asking that you assume liability; doing so exposes Tesla to unnecessary risk.
I didn't see an issue with signing the thing when I took my test drive. Yes, I read it and, yes, I knew exactly what it meant when I signed it.