As a level II Michelin certified tire technician, (I took my courses for aircraft but they cover everything) I'd never do it. Far too much goes into design of tires for a specific use for me to try to out think the people that design tires. Yes, many people will shell out 20K and up for a big heavy bike and then bitch about the cost of a tire. I have 2 words: fuck em. Let them do what they want. As far as no reported accidents or incidents with car tires, if the darkside web site is your source, there is none, but they exist. I personally know of 3. One dismount of a tire while turning, and 2 with sidewall to tread block seperation. Car tires might be designed for more weight, but no auto tire is designed to stand up on the edge of the tread block like the on in that pic.
I've read where folks say they have asked thier insurance carrier if it was a problem to insure, and they said no. Ask an adjuster or a complaintant's lawyer or investigator in an at fault accident, and you can bet all that money you saved on not buying motorcycle tires better be saved up for the judgement. Every DOT tire has a master list of wheel sizes and design codes it is certified to perform with, and motorcycle and passenger car wheels are NOT nearly the same. Take a 14 ply nose tire off a Boeing that is designed to slam into the ground at 400 feet per minute descent rate and accelerate from zero to 110 in less than a second and try to drive down the road with it on a pickup truck (similar dimensions to a 235/75-15) and it overheats and explodes within 10 miles. Not the job it was designed for. Fuck dark side ignorance. Peer pressure tightwads who believe thier own bullshit. I've ridden 2 bikes with car tires on them and they were both handling pigs.