A Silly Anti-Disassembly Trick
This is only a limitation of the demo version of Hopper.  The full version can disassemble itself, and it's not even prohibited by the EULA, unlike most software EULAs which have boilerplate no-reverse-engineering clauses.This behavior, both the technical and legal aspects, originated with IDA.  In fact, IDA's EULA has a clause explicitly permitting you to reverse engineer it (whereas Hopper's just doesn't mention reverse engineering).