But there are blind spots, as there are with everything on the road (even bikes). You can usually work with them as a lorry driver - I've never failed to see a dozy cyclist bimbling up the inside of my trailer as the traffic lights change, hemmed in on the other side by a pedestrian fence, while I'm indicating left (happened in Cardiff last year) - because you constantly scan the mirrors, you're aware that you overtook a cyclist not half a mile back and are looking for him, or whatever. Not all lorry drivers are as cyclist aware as me, though, even though they should be.
But ... start driving around urban environments on a dark winter evening, when your mirrors are spattered with rain and it's rush hour and every car has two bright lights which are refracted by the rain on your mirrors and which are much brighter than the average bicyle front light (and I'm being charitable and assuming that the cyclist is lit in the first place; again, there are plenty who don't bother) and you can perhaps start to see why I believe that anything which educates vulnerable road users as to why it's not a good idea to put themselves next to a lorry is a good thing. Yes, ideally road vehicles wouldn't have blind spots, and ideally all freight would go on the railways and canals and everyone would use bikes. But that's not how it is, and personally speaking I'd sooner deal with one artic driver than 40 transit van drivers any day of the week.