If you rely on radar when you shouldn't rely on radar, people can die. So the answer to half your question is that even a minuscule probability of misidentifica

If you rely on radar when you shouldn't rely on radar, people can die. So the answer to half your question is that even a minuscule probability of misidentification has intolerable consequences. If you rely on radar, because you can't rely on vision, people can also die. You are driving while blind to things like stop lights. Unless vision conditions improve it isn't safe to drive. Also there are going to be the same edge cases where radar failed, but now vision won't be able to compensate for them. Since radar can also fail by failing to detect something there, not just detecting something that isn't there, this is a fatality waiting to happen. In every other case, since the error bars are lower on vision than they are on radar, you ought to be relying on vision. Therefore, since in every conditional case in which driving is reasonable, vision is demanded, engineering effort is better directed toward vision than radar.