Many employers don't drug test. And many people in society aren't working for an employer that would test them anyway (e.g. self-employed, students, retired, etc.).
The reasons why it should be legal and the reasons why continuing to fight it as criminal are compelling on their own - regardless of whether the employers who test for it will change their opinion.
One possible change that could occur in this area is that the common urine test will be replaced by a method of testing (including a saliva test) that is more refined to the period of time in which the user will test positive. And other employers may choose to drop marijuana from their drug screening altogether (except in post-accident situations).