Prevent the police state by building the police state.
That being said: the PATRIOT act and NSA's PRISM program have shown just how blatantly the US Govt. can abuse individual privacy and rights so I don't think its a good idea. Weak crypto using backdoors is just a terrible idea period.
I guess what I'm trying to say is that the logic make sense in principle even though in practice it wouldn't work that way.
"The logic" in this case is a proposition about how beings behave. That is, "We can build the largest prison system in history, give law enforcement unlimited surveillance powers and not expect massive injustices." That is simply wrong. Human beings are not like that.