If you convict someone of a crime that they did not know was a crime, Because their ignorance about it was not a defense by law, They could get traumatized by the punishment and find it hard to get a job when they get out, Depending on the culture, And they could possibly commit suicide. It was not their fault that they did not know that their crime was a crime, You should blame the government for the justice system, For not having a system where people can take responsibility for their crimes when they are ready instead of when their old enough, And for keeping the education system out of date where not enough education about the law was taught. I do not think the government have any idea what ignorant people could be going through.
In an ideal world, This would be great - if you got pulled over while travelling through another state whose laws you weren't familiar with for violating traffic law, This would be very helpful. However, This excuse would be used by every lawyer in defense of their client until the end of time.