Families are complex, and schools need to accommodate them. Sometimes only one parent should have the ability to sign for their child. Unchecking the "Responsible signer" box only locks them out of contracts.
There needs to be a way to lock them out of signing forms (and any other permissions, such as applications) without stopping them from viewing student progress, schedule, &etc.
This would also be useful for families where other family members (such as grandparents) have been given permission to view student progress, even if they are not the legal guardians.