You can make the argument with the long-term benefits. But you cannot make it without proper statistically sound evidence about the CURRENT safety of the system that you intend to test, for the simple reason that the other traffic participants you potentially endanger are not asked if they accept any additional risk that you intend to expose them to. So you really need to be very close to the risk that they're exposed to right now anyway, which is approximately one fatal accident every 80 million miles driven by humans, under ANY AND ALL environmental conditions that people are driving under. That number is statistically sound, and you need to put another number on the other side of the equation that is equally sound and on a similar level. This is currently impossible to do, for the simple fact that no self-driving car manufacturer is even close to having multiple hundreds of millions of miles traveled in self-driving mode in conditions that are close enough to real roads in real cities with real people. Purely digital simulations don't count. What can potentially count in my eyes is real miles with real cars in "stage" environments, such as a copy of a small city, with other traffic participants that deliberately subject the car to difficult situations, erratic actions, et cetera, of which all of them must be okay with their exposure to potentially high-risk situations.
Of course that is absurdly expensive. But it's not impossible, and it's the only acceptable way of developing this high-potential but also highly dangerous technology up to a safety level at which you can legitimately make the argument that you are NOT exposing the public to any kind of unacceptable additional risk when you take the super-convenient and cheap route of using the public infrastructure for your testing. If you can't deal with these costs, just get the fuck out of this market. I'm also incapable of entering the pharmaceuticals development market, because even if I knew how to mix a promising new drug, I would not have the financial resources to pay for the extensive animal and clinical testing procedures necessary to get this drug safe enough for selling it to real humans. Or can I also just make the argument of "hey, it's for the good of humanity, it'll save lives in the long run and I gave it to my guinea pig which didn't die immediately, so statistically it's totally safe!" when I am caught mixing the drug into the dishes of random guests of a restaurant?