This is an apt reminder that the question is not "how likely is it that backdoor keys will be leaked/stolen?", but rather "how soon until the first backdoor keys are leaked/stolen, and how frequently after that?"
And to make it much worse, we would now also have to ask "how soon until the required systemic weaknesses themselves are used an attack vector for a mass breach?".
Just for a moment, ignore all arguments about citizens' rights to privacy, potential for abuse by the organizations authorized to access the secrets (and their many fallible and corruptible employees), and so on. Of course all that _is_ important, but just for the sake of argument, ignore it. The problem remains that if anything resembling the "EARN IT" bill passes, then attacks against encryption will _scale too effectively_, and the USA will have exposed itself to having the secrets of thousands of politicians and civil servants leaked to an adversary at once. What do you think happens to democracy when that happens?
I get that many people are short-sighted, or even simply apathetic to the long-term consequences of a law that might make their job easier today. But it seems that whenever computers are involved, lawmakers become _so_ incredibly short-sighted that it verges on madness.
Consider this: a bill requiring a small GPS and remote-controlled bomb to be installed in the engine of every car would allow the police to entirely avoid dangerous high-speed pursuits. If it could be done cheaply enough, should it be done? It's pretty easy to understand the myriad ways this could be abused, so it would never happen. But add computers to the mix, and suddenly any kind of foresight goes out the window.