All PC games until a few years ago where by default toggle aim, hold to aim is a by-product of porting a game from console to PC without the proper controls because all modern console game use hold to aim and they usually forgot to add toggle to PC.
I'm sorry but if you aren't capable of holding down right click when you want to ADS then you may wanna take up golf or something because PC gaming just isn't for you.
I'm not sure if this has been in other PC games and I just haven't noticed it but it seems like a stupid feature and a waste of time to allow it.
