For me its not just about criminal activity of their actions, its the lack of care, the lack of trying to check their own systems for errors. And then afterwards the attacks upon subpostmasters and what they were saying, not wanting to pay compensation, not actually clearing up the final remaining cases.
The rules they operate under (In my experience) are archaic, they treat their staff, customers, mail/parcels with contempt, as if we should count ourselves lucky they deliver stuff for us. Their police force, investigations team, still think they are working for the queen/king and treat staff/customers as such.
For me its been one of the shoddiest businesses I have worked for where things are literally held together by elastic bands. Yet staff are held to account if we dont deliver. Dont get me wrong, I love my job but its been an eye opener working for them.