For me, it's that the sponsor need have no experience in education and no roots in the local community which sits very, very uneasily.
Also, how undemocratic forced sponsored academies are.
In the economically poor part of the borough where I live, there isn't a single school judged to be 'outstanding', though a few judged 'good'; the great majority are 'satisfactory' or below.
In the wealthy part of the borough, all schools are judged 'outstanding' or 'good'. Leaving aside the obvious point about home influences, in academy terms this means that parents in the wealthy part of the borough get to be consulted with if their school wants to convert (or someone wants to convert it). They will have an opportunity to sit on the governing body and, though parent governors, have some say in some decisions about the school. These decisions will be taken by a group of people (the governing body) who come from various backgrounds, with different areas of interest and expertise.
Parents in the poorer part of the borough face their children's school being forced to convert against the wishes of the governing body, staff and parents, with no parental or community representation on a governing body. Even if it's improving and, now, even if it's 'satisfactory'.
This disparity sits very uneasily with me - it's like saying some parents/communities have the right to a voice and others just don't count.