Here is two reposts as this have been discussed in several old threads:
FLIPABLE SCOPES 1/2
Hi, the reason for not giving all these options in games (for example cs:go or Insurgency2014), is because it makes the game less gear choice dependent. A sniper is very lethal in bigger open areas, and the trade off is that in close quarters they are forced to use a pistol. Game becomes less class-dependent and because of that also less team-oriented and more all-round when introducing 1x sight feature no matter your scope. So when you choose to be a sniper oriented player, you know that you will be most effective on your team when covering the open grounds and trying to avoid cqb if possible. This balances the classes, or everyone would use a long-range scope, because of no drawbacks.
Also remember that you can switch weapon with the enemies you kill, so if you want to change role mid-game, you can time it with a kill. It is of course a question of taste, but personally I wish the game was even more class dependent to increase (and force) different types of play-styles."
FLIPABLE SCOPES 2/2
Bolt-action is not very good in cqb, even iron sight, I agree with that - better than pistol though.
Not saying it eliminates classes, just changes the weight towards less class specifications. Points are numerous already, many players with an offensive playstyle like me don't use armor or extra ammo in most cases anyway, because speed is so important for me- unless push playing where a bunch of frags is key where I want 2 frags in most cases.
Just saying with a system where you can flip away the long range scope, the new meta might be many more players using long range scope to both rule the open field and cqb, cqb bolt-action iron sight is one thing, semi-automatic a different story. I would probably put all points towards a mk 14 EBR high magnification scope, no armor, no extra ammo, no whatever to get that loadout and rush flanks + obj being happy with that in all situations - A lot of others might as well and the classes then be less significant, if that happens.
Maybe that does not matter, it would probably be a fun experience anyways - Who am I to judge. If a lot of players want this feature and more people enjoy the game - Cool. It could maybe be tested for an extended amount of time, then changed back if the impact is badly received, or then limited to coop.