As a teacher, I agree grades should reflect mastery. The goal is for all students to master the curriculum. If the majority of my students do poorly on an assessment, I know my teaching did not provide an effective learning experience, and we start over.
Most times the students who are not successful fall into two categories: students who are grade level(s) behind or who have difficulty with learning in general and those who have the ability but choose not to put forth the effort and/or do the work required.
Grades should reflect a degree of mastery. An A should mean a high level of mastery. All my students are given a reteach/retake opportunity for a maximum grade of a C. If the assessment was valid, those students needing re-teaching are not A or B students on that particular assessment.
The expectation of our school community should reflect the desired character traits of responsibility, integrity and perseverance. Adjusting our school system to eliminate failing grades or deadlines for work creates an environment of low expectation. As these young people make their way in the real world, will this model serve them well?