Don't be fooled into thinking its only birders who show a disregard for the welfare of rare breeding birds and ignore on-site instructions. Photographers are equally guilty, and in my experience probably more so.
I always associate the term 'birder' as meaning both observer and photographer, people who have an interest in birds, either to observe or photograph. Being both myself, that is how I read the post but someone always has to have that extra dig at photographers these days... :C
Having witnessed diplorable behaviour by both photographers and 'birders' (those without a camera :t

I would not catergorize one as worse than the other when it comes to the consideration of birds!!
Having witnessed an older gentleman (well past retirement age) walking towards a Short-eared Owl perched on the ground in Suffolk last winter, continually shouting to his wife "Can you see it yet", he continued toward it until surprise, surprise he flushed it; birders clambering through the bushes at the entrance to Horsey Gap car-park to flush out a Radde's Warbler so they could get the (all important) tick on their list... to more recently birders (both with and without cameras) tape luring the Wood Warbler at East Wretham so they could again 'get a good look' at their latest year tick!!
I suppose you have to put it down to Human nature and those who must see/photograph the bird at any cost, to the peril of the bird or other observers, they simply do not care about anyone else and certainly not the birds!!! It's very sad.