Why required and optional is removed in Protocol Buffers 3

The usefulness of required has been at the heart of many a debate and flame war. Large camps have existed on both sides. One camp liked guaranteeing a value was present and was willing to live with its limitations but the other camp felt required dangerous or unhelpful as it can't be safely added nor removed. Let me explain more of the reasoning why required fields should be used sparingly. If you

[akatakun]

proto3ではデフォルトでフィールドはオプショナル