If so, you'd be unable to do two things at once holding a sword. As for now you'll be able to for example hold a sword in one hand and a throwable potion or an enderpearl in the second. Once you right click you'll throw the potion or the ender pearl. You really want to not have this ability?
Why not only being able to block with a sword when you have nothing in your offhand? If you had something in your offhand right click would use the item in your offhand first.