The same argument can be made for smoke grenade since it clouds people's vision of an area, which can give a traitor time to kill and run away or prevent you from seeing where you go. etc. etc.
The line has to be drawn somewhere. Based on the rules, I think it's clear where the line is drawn.
Smoke grenades are not as intrusive.
Think of it this way. Someones throws a smoke, you can still kinda seen people as you walk through and mouse over people in the distance cause their name will pop up. You can clearly still hear if KOSes are called out or if there is discussion.
If someone throws a flash, not only can you literally see fuck all because it blinds your entire screen, you also can't hear a single thing. You can't hear if a KOS is called or if there is important game discussion going on. It is far more detrimental than a smoke grenade.
IMO flashes should be traitorous as they are far more detrimental and harmful than a simple smoke. Smokes you can still semi see through especially when you're walking through them. Flashes are disorientating and make it impossible to do key things in the game, like being able to hear KOSes.
It's just as much of a disadvantage to the Ts when someones throws one randomly. Everyone is flashed
Just like Frags or incends, they are just as detrimental to both as they can also kill T's which is why people should warn in chat before they through flashes just like they would any other grenade.
Its not a hard change to implement and I think it's something that should.
+1 on the idea.