for starters that hpa's have binary triggers, can't account wolverine and redline solenoid systems but the mechanical and polarstar systems don't.
also that all hpa users are cnuts, because they aren't......
to add to the list lets address the 3 main arguments that tend to get levied against hpa:
high rof- just have an rof site limit- the hpa guys can turn their guns down, not so easy for a dsg build without a fancy mosfet......
joule creep- chrono on joules, gbbr's and heavy piston'd boltys have the same problem, also if i had a penny for every site that didn't chrono green gas pistols.......
reg twiddling- a lot of hpa regs can be tournament locked, the qc spring on a scorpion evo (other qc spring guns are available) can't, jus' sayin.......