In a clash of deeply felt testimony, parents in tears pleaded with Colorado lawmakers on Friday to pass a bill allowing their children with autism to use medical marijuana as a treatment. “I’m begging you to approve this bill,” said Jamie Kropp, whose son, Kolt, has autism. Psychiatrists and the head of the state Health Department, though, opposed writing such a permission into law, saying there isn’t enough evidence to know that cannabis would do more good than harm, even though they sympathize with the frustration families feel. “There is no easy answer,” said Dr.