I think repeatidly slapping them with a pretty soft plastic attraption until they stop moving is even harsher though.
Or slapping them outta the air, trying to electrocute them but having too little power on the shitty device so only their wings get burned.
Or vacuuming them up
Or flushing them down the drain.
Honestly, whatever people usually do to them it's way way crueller
It's soft to you, not to the fly. You don't slap a fly "until it stops moving". When you swat a fly, it explodes.