The operative word there is "should", that indicates a personal opinion not a fact. If you say no one "should" pull into an intersection you have to assume it is for safety reasons. Then by that logic (because of the safety factor) no one "should" drive due to the dangers of doing so. To extrapolate that logic, no one "should" leave their house due to the possible dangers and for that matter no one "should" live in a highrise due to the fire hazards and for that matter, no one "should".......get where I'm going with this?
See, the thing about those lines at intersections: they are designated so that you stop there on a red or an amber. NOT on a green. If the light is green you proceed to make your manouver, whether it be driving straight through or a turn) and then stop if and when it isn't safe to proceed. If the intersection is blocked, then no, you shouldn't pull into it and cause more of a log jam, but to naturally assume that you won't be able to make the turn during the course of the green would cause a traffic jam for miles.
(but this is another example of why roundabouts are THE way to go and for that matter, secondary turn streets NOT at major intersections is a underutilized concept. This is where you cannot make any turns at a given intersection but use a side street 1/2 block before or after the intersection). If you know the bloor and church intersection there is a small side street just east of church, north off bloor. If you have to turn North or South on Church, you turn down this small side street and 9 times out of 10, you can complete the turn without having to pause for traffic. This is easy to do because the majority of pedestrian traffic is due to the office building on the corner of Bloor and Church. 1/2 block away, very little pedestrian traffic. It is rare to be able to make a right turn there without having to stop for the entire light due to pedestrians.....