The back door isn't going to be built into super encrypted military stuff, but a lot of government traffic travels over commercial links, using commercial hardware and software.
Since this government backdoor is going to be leaked or hacked about 3.2 femtoseconds after it's introduced then every internal government memo, every cell phone/sms between a politician and their mistress or lobbyist and every conversation between lawyer and client is going to be on wikileaks.
We could finally have real democracy!
SPOILER ALERT
Marlo (the drug lord) sent picture messages of a clock to arrange meetings. The hour and minute hands corresponded to the letter and number axes of a common Baltimore map and the second hand tells what page. The dealers would look up the coordinates on a map to find out where to meet. The cops broke it because they had (illegal) wiretaps on everyone's phones, and they had illegally allocated lots of extra manpower to tail all of the suspected drug dealers around the clock.
END SPOILER
According to "The Wire" they often even put extra layers of encryption security, anyway. Such behavior would make that legislation even more useless, as it would indeed only target the innocent that don't take extra precautions.