Reasons not to consider PGA-style program algebra

There are many reasons for people not to spend any time on PGA and its style of program algebra. Of course reasons are not required for ignoring this work. For me it is important to understand these arguments and a listing might be useful for others as well. In practical terms it is a big advantage that no other researchers (i.e. groups outside the UvA) are working on PGA as it makes life more easy-going, and provides a better opportunity to set out a long term project in a number of steps. There is a disadvantage as well, of course. Peer groups in the same area can provide a more productive context altogether and can (but need not!) prevent one from digging into futile depths.