Why internet back door laws are not a good idea

As I mentioned earlier, there is a proposal in the US for legislation to require backdoor internet access to law enforcement.  There have been similar proposals in Canada for "lawful access". Bruce Schneier has a good post entitled Wiretapping the Internet that explains why this is a bad idea.  The entire post is worth reading, but to give a flavour:

These laws are dangerous, both for citizens of countries like China and citizens of Western democracies. Forcing companies to redesign their communications products and services to facilitate government eavesdropping reduces privacy and liberty; that's obvious. But the laws also make us less safe. Communications systems that have no inherent eavesdropping capabilities are more secure than systems with those capabilities built in.

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Official misuses are bad enough, but the unofficial uses are far more worrisome. An infrastructure conducive to surveillance and control invites surveillance and control, both by the people you expect and the people you don't. Any surveillance and control system must itself be secured, and we're not very good at that. Why does anyone think that only authorized law enforcement will mine collected internet data or eavesdrop on Skype and IM conversations?