Why? Seriously. Is it toooooooooo muuuuuuuuuch to wait a second for the scan to complete before you pew pew pew? Smart pilots might see the scan completion time as an opportunity to line up their shot and charge their railguns.
I see what you're saying, and it's a tough one to call because I understand the limitation of the mechanic: you need clearance to fire. I'm more or less used to just watching the scan thing now and controlling my itchy trigger finger, although the odd slip still occurs and I have to boost out of there.
Usually, though, it means watching them go at it and miss out if they get him first, or if he manages to escape to supercruise. So there is this sort of cognitive dissonance when a pirate wing is attacking an innocent miner, or a group of security are wearing down a pirate, and you still have to sit idly by until your scanner is happy that the guy is definitely Wanted.
I think the suggestions are really to just tweak that part of the game a bit so it flows more rationally while you're immersed in the world. Perhaps, if an attack is in progress already then the scanner could just skip to the result immediately without the wait, as if it has fast-tracked the approval by recieving the data from the other ships that have already scanned them?