Thats a mighty broad brush your sweeping with there. I have some certification and experience in the attack side of things, and also the same from the blue arena, and I have never ever advocated back dooring anything. In fact I've worked to have them removed from bits of infrastructure and devices in the past when others were wondering "why don't we repurpose that..." I carefully explain to them that if I put a backdoor into something that can be used but makes my life easier, so can anyone else, and they can also use mine if they find it. Post test exploit cleanup should always remove all of your tools and code used to perform the exploitation leaving nothing behind to indicate you were there.
I don't think anyone really competent down in the trenches with the right amount of experience thinks its a good idea, its just someones idea to save effort higher up.